I have import an Music XML. There is a eight note at the end of an bar tied to a half note in the next bar.
Shorten this note with Shft-Alt-Arrow < give a strange (!) value on the last beat of the previous measure.
Lengten this note first with Shft-Alt-Arrow > and after that shorten will work perfect.
See GIF (I have press UNDO before lengthen the note)