The live character count isn't quite accurate. For example, each newline is actually two characters, but the live count counts it as only one character. So if you have "11 characters left" in 56 lines, then you're actually going to be at least 44 characters over the limit. Fitting things to the limit requires some trial and error. In this case, it might work to just remove the unnecessary newlines from your signature.

Your signature was cut off before, but you didn't notice this because the forum tried to fix your incomplete bbcode and was apparently mostly-successful. To prevent the bbcode parser from generating invalid HTML (which was causing trouble), this is no longer done in some cases. It's not going to be changed. You'll have to fix your signature.