And I am must getting up.
If you have any stylesheet tiddlers, I'd check and see if there is any conflict with this new CSS we are playing with.
Also, if you do have any stylesheet tiddlers that you've created, check to make sure you don't have any missing closing curly brackets, i.e. "}". A missing closing curly bracket will immediately end sequential processing of all stylesheets from that point.
Next: conflict with any missing plugins?
Next: any chance that you or a plugin has somehow altered the tc-image class such that it can't be resized? (I'm reaching.)
I can't think of anything else at the moment. Gotta get some serious caffeine into me. Well, after I ride Algea for 15 minutes (my stationary bike). And then scrub an armpit or two ... Yeah, it's a process.