I am running trunk, which I think is currently identical to 3.3.1 and it crashes on the first request. FC 18, forward full transparent, null transform enabled. It seems to work without the null transform, though. The error is at P_ProtectionQueue.h:90 with a failed assert. Running in the debugger gives varying results about whether the value in the assert is actually wrong, which suggests a race condition.
Compile with DEBUG and WCCP enabled. To reproduce I set for forward transparent, enable the null transform, and then make a request for a ~17M file. It generally fails within the first 1M or so. I'll look some more tomorrow.