Tweetie is probably the best Twitter client out there, but it has an annoying bug. Yes, the dev says it's Twitter's fault, but it's frustrating to the average user and no other Twitter client has this problem. Even deleting my entire avatar cache did nothing to bring on my new avatar. Yes, I uploaded a 640x480 profile pic (people should be able to see a larger version when they click on your avatar).
I just tried uploading a smaller avatar to test (<200 x 200 px), however, and it did nothing. Deleting the cache again did nothing. Come on dev...fix this BS. I shouldn't have to reinstall the app to get my avatar back. You're charging for this app, so please do your work.
Twitter has been having issues with profile images recently. It turns
out, if you've updated your profile image in the last week (and it was
a big image) it wouldn't be scaled down properly.