A coworker asked this question. Unfortunalty she works about 2,000 miles from me.
The delete key on her keyboard is suddenly bringing up the "fill" box.
My guess is she somehow changed the keyboard shortcut from "shift F5" to delete.
Any other way this could have happened?
Your coworker will have a selection and Background layer targeted when delete and backspace keys bring up Fill dialog. That's because Background doesn't support transparency, so something has to fill the region being deleted.
Hmmm. I thought the delete key acts as a "fill with background color" if you are working on the background layer. Is that now so?
In CS6 and CS5.1:
Fill with background colour is Cmd/Ctrl with backspace or delete, for Background or other pixel layer.
Fill with foreground colour is Opt/Alt with backspace or delete, for Background or other pixel layer.
I don't know about earlier versions.
Same with CS5.
The default behavior of the Delete key was changed with the introduction of Content Aware Fill in Photoshop CS5, and it still brings up the dialog in Photoshop CS6 (I think there was a misunderstanding above). Adobe's rationale must have been something like "now there are multiple ways to do fill, so we need to present those options to the user."
The only way that "suddenly" the behavior could have changed for badchess' co-worker is that either she "suddenly" began using a new version of Photoshop or she "suddenly" started doing operations on a Background where she had been working in layers before.
As I said, I have CS5 and CS6 at home, but at work I am running CS4 telling someone else how CS5 should act.
Not sure why she just now noticed the change in the way the delete key that occurred between CS4 and CS5, but all is well.