I've been using Inkscape off and on for years, for laser cutting designs where object positions need to be precise. My method for positioning objects is to select the object, then enter the desired x and y coordinates in the X: and Y: boxes at the top of the screen. This sets the position of the upper left corner of the object.

Today I installed Inkscape on a new machine, and it looks like it's a more recent version (cosmetic differences from what I'd been using). It worked fine at first, but then, while I was in the middle of working on a file, the above behaviour suddenly changed. Now, the Y: box still refers to the top of the object, but the X: box refers to the middle of the object instead of its left.

I must have hit some sort of keyboard shortcut that changed a preference setting. I don't know if it was just bad luck, or if the keyboard shortcut is new in the new version. Either way, I can't figure out which preference I changed so I don't know how to change it back. Please help!

Maybe this: https://wiki.inkscape.org/wiki/index.php?title=Release_notes/1.2#Selector_Tool

Also, while the object rotate handles are visible, clicking on the rotation center will set the anchor point to the rotation center. Clicking on the rotation center again will restore the anchor to the upper left.

(Shift click on the rotation center will return it to the object center if it has been moved.)

Thanks! The selector tool sounds like it's probably it.

Embarrassingly, I forgot to try just closing Inkscape and opening it again (!) So when I opened it to try out the selector tool, the problem had already fixed itself. But if it happens again, I'll try the selector tool first!

It happened again, and with the help of the above answer I was able to figure it out. I'm posting the complete answer here for the benefit of anyone who comes across the thread looking for the solution.

It turns out that when the rotation handles on an object are visible, if you click the rotation center it will set the anchor point to the center for all objects, not just the one you've selected. So if you then select a different object, the anchor will be in the center. The solution is equally simple - select any object, click to display the rotation handles, then click the center again to set the anchor back to the upper left for all objects.

When googling for a solution previously, I'd found the rotation center thing but didn't think it applied because I was dealing with a setting applied to all objects, and the rotation handle thing seemed to just be about a single selected object. It's a bit weird that it affects all objects that way, so hopefully this post will help others having the same confusion.

Thanks for sharing the details.  👏  If it happened to you, I'm sure it will happen to others.