UI changes are ignored; wrong forms are displayed at runtime

After making significant changes to a form in Creator, I was baffled by their lack of effect in the app. I noticed that labels on my form contain totally incorrect text; they're showing old content that has been replaced in the form designer.

The XML for the UI reflects my changes... so where are these values coming from? A project-wide search for the erroneous strings turns up nothing.

I then used a file-search utility to search for the strings, and found them in the ui_ file for the afflicted form. For some reason, these are not being kept in sync with the UI design.