We know about these problems; they're in the When Things Slow Down™ list. (As all telephone hackers know, in-band signaling is a bad idea.)
I think the %varname thing was originally a bug, but it turned into a feature because it turned out users like it as a shortcut. But I seem to remember we had added a special case so that % as a word all by itself would work as the user intended. But apparently there has to be some text before it to work! You learn something every day...