I don't know when it changed but in my jump from Xara Designer Pro X11 to X16 I found that there has been a change in the way bitmaps are stretched when being resized along only one axis.

I've used the Xara drawing software almost daily for 20 years so suspected that there'd be a way to stretch a bitmap somehow - but couldn't find anything in the right-click menus, the regular File/Edit/Arrange/etc menus, nor in the Status bar's tips.

I found it as Alt+drag by guessing. I suspect that change has been made and you forgot about the Status bar. It tells us of how Shift+drag and Ctrl+drag affects things, but not Alt+drag.

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