If its the bug I'm thinking it is, then you will get 50 attempts, but not 50 shares. If its the bfi_int harmless driver bug, then you will get 50 shares, but way more than 50 attempts.
So I started up diablo and after 14 minutes:
* 42 attempts
* 31 shares
* 273378/271347 khash/sec | ghash: 226,4
Not sure if this will help you track down what is going on with my setup. It looks like it's the "bad" bug, not the harmless bug. That would explain why the deepbit hashmeter never ever reached more than about 200mhash/s.
Maybe I'm just trying to get more out of my hardware than I should, thus really causing a "possible driver or hardware issue"?
edit: I also modified diablominer so it will send attempts even though H != 0, but that didn't work of course (ERROR: Connection failed: Bitcoin returned error message: Wrong data: checkWork: checkHash wrong).