Hi,
there is an error : convert: sol2.tif: unknown field with tag 37724 (0x935c) encountered. `TIFFReadDirectory' @ tiff.c/TIFFWarnings/703.
Do you know what that can mean?
It seems to be a known bug in imagemagick, supposed to be fixed back in 2008 and 2010. For what I understand it seems related to a layer count/index bug. Try to paste your picture in a fresh-1-layer picture to see if that helps.
Also sound like a good time to introduce Gimpshop to your students :).