OK, to answer your questions:

1. "Do you have one with an 'original' value of '1'?" YES

2. "Does a file with that 'filename' exist in your 'avatar' folder in the GNU social root?" YES. In fact, here is the link to the goofy profile photo I uploaded: https://chirp.cooleysekula.net/avatar/3-382-20140803173753.png

3. "Has any other 'width' (or height) values than the one from 'original' been generated?" NO

4. "....also, what happens if you turn of the #Gravatar plugin?" IN PROGRESS