The order of values on the stack is backwards for RAISE_VARARGS.  The docs say:

"Raises an exception. argc indicates the number of parameters to the raise statement, ranging from 0 to 3. The handler will find the traceback as TOS2, the parameter as TOS1, and the exception as TOS."

But in fact, the order is reverse of that.  In the one-parameter case, the exception is TOS, in the two-parameter case, the value is TOS, and in the three-parameter case, the traceback is TOS.  Not sure how to write that concisely, thought.  :)