[trunk] tremolo cannot be added

Windows R5311.

Steps to reproduce:
1) create new score (4/4 time)
2) add two minims (1/2 notes) into the first bar.
3) drag a tremolo symbol onto the first note.

Expected result:
1) both notes change to whole notes
2) the tremolo is drawn somewhere in between them

Result:
The wrong symbol is drawn on top of the first note. The note values don't change.

May be related to issue #14836: [Trunk] Tremolo appear with one stroke under each note