Hitting backspace when the move dialogue box is showing ends up applying to the document, not the text in the “select and item to move to” box. It seems this only happens when the cursor (on the document) is at the start of the line when you use the move shortcut.
It looks to me like the merge lines code is running without considering the move popup box… so it might also happen for other popups.
This can lead to loss of data by merging two lines together (when notes are used and the lines merged, the notes from the second item seem to be discarded).
I use the move command frequently to tidy my document so this happens to me very regularly.