I've answered to this one on the github repo, so here is a copy-paste of that.
Pixate work on AdapterViews by proxying them in order to tag the recycled views with their new position (see https://github.com/Pixate/pixate-freestyle-android/blob/master/pixate-freestyle/src/com/pixate/freestyle/PXHierarchyListener.java#L232 ). This allows us to style more complex CSS expressions, like "nth-child" on a list. Currently, that java.lang.reflect.Proxy is being created with a few known adapter interfaces, so the casting will fail if you would like to get your original BaseAdapter.
The good news is that we have a way to get to that original Adapter via PixateFreestyle.getAdapter(AdapterView view). Then you can cast to your BaseAdapter. That should not cause any problem.