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.
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).
colStore.proxy.url = colStoreUrl;
Maybe this helps a little more.
Moved this over to the Bugs forum. Additional report adding to your notes:
I have same problem for infinite grid, does anyone know what causes this error?
Uncaught Ext.data.PageMap.getRange(): PageMap asked for range which it does not have
Don't know exactly what caused the bug/issue but I submitted a support ticket referencing this thread. Last week they replied with the problem will be fixed in the next 4.2.x release. I haven't heard yet when that is scheduled.
FYI: Provided there are no blocking issues in the very near term, the release date for 4.2.2 (Premium subscriber release) is September 19th.