The header part that says D&D Compendium is a giant waste of space, it could be much skinnier and still iconic looking along the top.
Races/Classes, and Powers/Skills links could move up to be in line with the other links. Search button could move up next to the search text box, and the reset button to its right.
The filter group box needs to be visible only for the creatures, items, and powers tabs. It can be hidden the rest of the time.
White space in the result list could be reduced just a little.
Center the page if the browser form is wider.
This would be my immediate UI advice if this was presented to me as a proof of concept. The tightening up of the group boxes will result in less scrolling. Right now eventhough I work on a fairly high resolution screen I have to scroll every time I do a search. On a laptop, I'm sure the amount of scrolling one has to do would be quite annoying. As for functionality issues...
When a search is in progress or a filter is being applied, there needs to be some indication of a work in progress if it's going to take more than a split second. Currently, you're left wondering if you actually clicked anything.
Item filters still don't work.
While a better copy/paste feature would be nice, it's not really so much a bug, since it wasn't a feature to begin with. It's just the way "copy" picks up formatting from a browser. It was working better before than it is now, but that's not by design. A wysiwyg copy/paste into word or excel would be pretty sweet, but I doubt they will go that route.