Think the reason for any jagged edges, etc. might be in the method chosen for uplifting the original file(s) to the server. I had a similar short term problem with Photobucket. A lot of these services are trying to resize, compress and generally force your nice square picture into their nice, round box. Have you changed the uplift method in recent times?
All you need do, is drop them a line and explain briefly, your perception of the problem and ask if they have another uplift tool. Bet that sorts it :-)
Let me know - am interested in this one :-)
Conan