Backup moves tremolo up

When a tremolo is placed between 2 notes of which one to the reoriented stem is voluntarily or by presence of notes of another voice on the staff at each save the tremolo moves upwards.

So to observe the phenomenon:

1 - open this file attached : 01 trem.mscz
2 - visually locate the position of the tremolo ( or see vertical position in the inspector )
3 - save the file
4 - close it
5 - reopen it
6 - start over 2 ad libit.

If there is no backup (completed score) tremolo does not move.