Yes, I noticed this myself a few days ago. I think there are two problems.
The first is, the new version of phpThumb that came with MODX 2.2.12 may have a
bug which causes it not to size thumbnails correctly in this case. (pThumb just passes off the input image and parameters to either phpThumb or Resizer to do the actual work). I haven't looked into this one really.
But Resizer doesn't work correctly
either. It sizes the image to w x h, then tries to crop a sw x sh rectangle image out if it. But it should be the opposite order: crop first, then resize. Anyway, this'll be fixed in the next version. If you want you can replace core/components/resizer/model/resizer.class.php with
this version and it should work. Make sure you change the 'Use Resizer' system setting to Yes and clear out any cached images so that they'll be regenerated.