Awesome! I expected this to not be supported in some DBDs, but if it fleshes out bugs where it is supposed to be supported, then it's done more than originally intended!
Thanks for the example runrig. The problem was fairly specific in that it only went wrong it you called bind_param_inout with undef values initially then changed them to strings shorter than 28 characters. However, it was certainly a bug and I was a little surprised no one has hit it before.