I have run into this same problem and am wondering if any progress has been made. I am using 4.2 SDK and am doing the following in my code.

Code:
columnGrid.getSelectionModel().clearSelections();
colStore.data.clear();
colStore.proxy.url = colStoreUrl;
colStore.load();
It seems to only happen when I load the buffered store, then come back to reload the buffered store and 0 results come back. (I don't mean .reload() btw).

Maybe this helps a little more.