Dragging to reposition a symbol ("Z" palette) responds erratically on release

1) default score
2) add a symbol from the "Z" palette to the first measure rest
3) try to drag it

Result: when you release, it jumps somewhere else. Positioning via the Inspector works fine. Other elements work fine. I'll guess we are getting the wrong value for the base position somehow.

BTW, it's not about measure rests being special - same bad behavior attaching to a note.