in Ext 4.1 beta 2, the Buffered Scrolling grid example.

If I click on the Name column header to sort the names:

instead of getting "1 Tommy White" in the first row, I get "37 Tommy Spencer".
"1 Tommy White" appears about 15 rows down.
If I scroll down and back up, it is corrected, "1 Tommy White" appears in the first row.