diff --git a/web/skins/classic/views/js/montagereview.js b/web/skins/classic/views/js/montagereview.js
index 92ffb9849..a02e11d69 100644
--- a/web/skins/classic/views/js/montagereview.js
+++ b/web/skins/classic/views/js/montagereview.js
@@ -1316,23 +1316,29 @@ function loadEventData(e) {
           const op_name = 'filter[Query][terms]['+found[1]+'][op]';
           const op = this.form.elements[op_name];
           if (attr) {
-            if (attr.value==='Monitor') attr.value='MonitorId';
-            // DateTime is a filter-engine pseudo-attribute, not an Events
-            // column: Filter.php resolves 'DateTime' and 'StartDateTime' to the
-            // same E.StartDateTime.  The API takes column names, and silently
-            // ignores a term it cannot resolve rather than erroring, so leaving
-            // it as DateTime returns every event ever instead of the window.
-            if (attr.value==='DateTime') attr.value='StartDateTime';
+            // Translate to the column names the API expects, in a local rather
+            // than by writing back to attr.value.  The form is submitted when a
+            // filter changes, and montagereview.php decides whether the range
+            // terms are already present by looking for 'DateTime'; a form left
+            // holding 'StartDateTime' came back with a second, duplicate pair.
+            // Filter.php resolves 'DateTime' and 'StartDateTime' to the same
+            // E.StartDateTime, so only the query needs the column name.  The
+            // API silently ignores a term it cannot resolve rather than
+            // erroring, which is why an untranslated DateTime returned every
+            // event ever instead of the requested window.
+            let apiAttr = attr.value;
+            if (apiAttr === 'Monitor') apiAttr = 'MonitorId';
+            if (apiAttr === 'DateTime') apiAttr = 'StartDateTime';
             let urlVal = val;
             // Normalize date/time values to YYYY-MM-DD HH:mm:ss for the API URL.
             // Locale formats using / as separator break the URL path.
-            if (/Date|Time/.test(attr.value)) {
+            if (/Date|Time/.test(apiAttr)) {
               const m = moment(val);
               if (m.isValid()) {
                 urlVal = m.format('YYYY-MM-DD HH:mm:ss');
               }
             }
-            url += '/'+attr.value+' '+op.value+':'+encodeURIComponent(urlVal);
+            url += '/'+apiAttr+' '+op.value+':'+encodeURIComponent(urlVal);
           } else {
             console.warn('No attr for '+attr_name);
           }