After selecting any file you should see two identical results in both tests. It works fine in Mozilla Firefox 19.0 and Chromium 26.0.1383.0.

In Opera 12.14 both lines of Test #1 are identical, it seems Opera doesn't allow re-using FileReader with different readAsArrayBuffer argument. It's a regression since it was working fine in Opera 11.64 (Presto/2.10.229).

Test #1

Select some file

Test #2

Select some file