Create a quarter note, any note, in a score. Press keyboard "X" twice to flip the note-stem then flip it back again. Now use Shift + X twice to flip the note-head then flip it back again. Now press "X" once.
You will see that the note stem flips to the wrong side of the note.
Comments
This is correct. Pressing doesn't Shift+X twice does not restore the "auto" property of the note head - it fixes it to the original side of the note (left or right depending on staff line), as can be seen in the Inspector. With the note head now fixed to that side, it reamins on that side as the stem direction changes. If it didn't it would be a bug that fixing the note head to one side or the other didn't stick.
To restore the "auto" property, simply set in in the Inspector ("Mirror head").