Portrait orientation rotated - but not originally

Very strange behavior behavior today.
I went looking for some shots I took last year, and found them easily.
However, in the folder they were in, everything taken in a portrait format (rotated camera) was off.
The thumbnail was rotated 90 dg, the media view by 180.
Last year (last time I looked) they were all fine.

The strangest behavior was seen next. Photos in a different folder taken a day later were just fine.

Rebuilding didn't work.
The only fix was to remove them from the catalog, then re-import them. That fixed the orientation problem.