$! isn't guarenteed to be reset after a successful call. I suspect you're seeing an error message from a previous call.

If you look at the code, you see that $! is set before the call to move (it would generate a warning if they are turned on, but $! is still set to 0). $! will be set by move() (or by one of the function that it calls). You just shouldn't draw conclusions from it.

Abigail