Move m_playingNotesMutex.lock() and m_playingNotesMutex.unlock() outside of if( m_playingNotes.indexOf( _n ) >= 0 ) Conflicts: plugins/sf2_player/sf2_player.cpp Remove note from m_playingNotes before deleting its m_pluginData in sf2Instrument::deleteNotePluginData() Move m_playingNotesMutex.lock() and m_playingNotesMutex.unlock() outside of if( m_playingNotes.indexOf( _n ) >= 0 )