diff --git a/services/search/pkg/opensearch/internal/convert/kql_expand.go b/services/search/pkg/opensearch/internal/convert/kql_expand.go
index 5688f6dfe6..5fd149f81e 100644
--- a/services/search/pkg/opensearch/internal/convert/kql_expand.go
+++ b/services/search/pkg/opensearch/internal/convert/kql_expand.go
@@ -3,10 +3,10 @@ package convert
 import (
 	"fmt"
 	"reflect"
-	"slices"
 	"strings"
 
 	"github.com/opencloud-eu/opencloud/pkg/ast"
+	"github.com/opencloud-eu/opencloud/services/search/pkg/search"
 )
 
 func ExpandKQL(nodes []ast.Node) ([]ast.Node, error) {
@@ -94,10 +94,12 @@ func (_ kqlExpander) remapKey(current string, defaultKey string) string {
 }
 
 func (_ kqlExpander) lowerValue(key, value string) string {
-	if slices.Contains([]string{"Hidden"}, key) {
-		return value // ignore certain keys and return the original value
+	// only fold the value for fields whose index analyzer lowercases too;
+	// case-preserved (keyword) fields must keep their casing or they never match
+	// their stored token. Shared with bleve via search.LowercaseValueFields.
+	if _, ok := search.LowercaseValueFields()[key]; !ok {
+		return value
 	}
-
 	return strings.ToLower(value)
 }
 
diff --git a/services/search/pkg/opensearch/internal/convert/kql_expand_test.go b/services/search/pkg/opensearch/internal/convert/kql_expand_test.go
index 49218d5aa5..6a62b151a9 100644
--- a/services/search/pkg/opensearch/internal/convert/kql_expand_test.go
+++ b/services/search/pkg/opensearch/internal/convert/kql_expand_test.go
@@ -244,7 +244,22 @@ func TestExpandKQLAST(t *testing.T) {
 	t.Run("lowercases some values", func(t *testing.T) {
 		tests := []opensearchtest.TableTest[[]ast.Node, []ast.Node]{
 			{
-				Name: "!Hidden: StringNode -> stringnode",
+				Name: "lowercase-analyzed field: value is folded",
+				Got: []ast.Node{
+					ast.StringNode{Key: "Name", Value: "StringNode"},
+					ast.GroupNode{Key: "GroupNode", Nodes: []ast.Node{
+						ast.StringNode{Key: "Name", Value: "StringNode"},
+					}},
+				},
+				Want: []ast.Node{
+					&ast.StringNode{Key: "Name", Value: "stringnode"},
+					&ast.GroupNode{Key: "GroupNode", Nodes: []ast.Node{
+						&ast.StringNode{Key: "Name", Value: "stringnode"},
+					}},
+				},
+			},
+			{
+				Name: "case-preserved field: value keeps its casing",
 				Got: []ast.Node{
 					ast.StringNode{Key: "aBc", Value: "StringNode"},
 					ast.GroupNode{Key: "GroupNode", Nodes: []ast.Node{
@@ -252,24 +267,9 @@ func TestExpandKQLAST(t *testing.T) {
 					}},
 				},
 				Want: []ast.Node{
-					&ast.StringNode{Key: "aBc", Value: "stringnode"},
+					&ast.StringNode{Key: "aBc", Value: "StringNode"},
 					&ast.GroupNode{Key: "GroupNode", Nodes: []ast.Node{
-						&ast.StringNode{Key: "aBc", Value: "stringnode"},
-					}},
-				},
-			},
-			{
-				Name: "Hidden: StringNode -> StringNode",
-				Got: []ast.Node{
-					ast.StringNode{Key: "Hidden", Value: "StringNode"},
-					ast.GroupNode{Key: "GroupNode", Nodes: []ast.Node{
-						ast.StringNode{Key: "Hidden", Value: "StringNode"},
-					}},
-				},
-				Want: []ast.Node{
-					&ast.StringNode{Key: "Hidden", Value: "StringNode"},
-					&ast.GroupNode{Key: "GroupNode", Nodes: []ast.Node{
-						&ast.StringNode{Key: "Hidden", Value: "StringNode"},
+						&ast.StringNode{Key: "aBc", Value: "StringNode"},
 					}},
 				},
 			},
diff --git a/services/search/pkg/query/bleve/compiler.go b/services/search/pkg/query/bleve/compiler.go
index b0fbeb870e..02f5c17992 100644
--- a/services/search/pkg/query/bleve/compiler.go
+++ b/services/search/pkg/query/bleve/compiler.go
@@ -8,26 +8,13 @@ import (
 	bleveQuery "github.com/blevesearch/bleve/v2/search/query"
 	"github.com/opencloud-eu/opencloud/pkg/ast"
 	"github.com/opencloud-eu/opencloud/pkg/kql"
-	"github.com/opencloud-eu/opencloud/services/search/pkg/mapping"
 	"github.com/opencloud-eu/opencloud/services/search/pkg/search"
 )
 
-// lowercaseFields is derived from Resource.SearchFieldOverrides(): any
-// field whose override picks a lowercasing analyzer (`lowercaseKeyword`)
-// or the fulltext type (which uses a lowercasing analyzer under the hood)
-// gets its query-side value pre-lowercased so compile-time matches the
-// index-time tokenization. Anything else keeps its original casing.
-var lowercaseFields = buildLowercaseFields()
-
-func buildLowercaseFields() map[string]struct{} {
-	out := map[string]struct{}{}
-	for key, opts := range (search.Resource{}).SearchFieldOverrides() {
-		if opts.Analyzer == "lowercaseKeyword" || opts.Type == mapping.TypeFulltext {
-			out[key] = struct{}{}
-		}
-	}
-	return out
-}
+// lowercaseFields holds the fields whose query-side value is pre-lowercased so
+// it matches the index-time lowercasing analyzer. Shared with the OpenSearch
+// backend via search.LowercaseValueFields; every other field keeps its casing.
+var lowercaseFields = search.LowercaseValueFields()
 
 var _fields = map[string]string{
 	"rootid":    "RootID",
diff --git a/services/search/pkg/search/search.go b/services/search/pkg/search/search.go
index 39ac50f704..6b2023b26f 100644
--- a/services/search/pkg/search/search.go
+++ b/services/search/pkg/search/search.go
@@ -88,6 +88,27 @@ func (Resource) SearchFieldOverrides() map[string]mapping.FieldOpts {
 	return resourceFieldOverrides()
 }
 
+// lowercaseValueFields is the set of index field names whose query values must
+// be lowercased to match their index-time lowercasing analyzer (lowercaseKeyword
+// or the fulltext type). Built once from the field overrides.
+var lowercaseValueFields = sync.OnceValue(func() map[string]struct{} {
+	out := map[string]struct{}{}
+	for key, opts := range resourceFieldOverrides() {
+		if opts.Analyzer == "lowercaseKeyword" || opts.Type == mapping.TypeFulltext {
+			out[key] = struct{}{}
+		}
+	}
+	return out
+})
+
+// LowercaseValueFields returns the set of index field names whose query values
+// must be lowercased so query-side matching lines up with the index-time
+// analyzer. Both search backends use it, so value casing stays consistent; every
+// other (case-preserved) field keeps its original case. Read-only, do not mutate.
+func LowercaseValueFields() map[string]struct{} {
+	return lowercaseValueFields()
+}
+
 // ResolveReference makes sure the path is relative to the space root
 func ResolveReference(ctx context.Context, ref *provider.Reference, ri *provider.ResourceInfo, gatewaySelector pool.Selectable[gateway.GatewayAPIClient]) (*provider.Reference, error) {
 	if ref.GetResourceId().GetOpaqueId() == ref.GetResourceId().GetSpaceId() {