v20 tries harder.
Seriously, we added some code so that the mouse-over would extract comments for all the symbol matches, definitions and declarations, because people want to see the comments and are very inconsistent about where they like to put them. Somebody asked for it. Not much of a problem when you just have a declaration and a definition (or a few), but more trouble if you have a symbol with 1000 matches. That's where the 1 second time limit comes into play. That is also a tunable parameter, in the Context Tagging options, BTW.