If letters are used for N, it evaluates to zero and returns $hget(hashtable, 0).data, rather than return $null or throwing an error.

The same is true of virtually all of mIRC's identifiers - bad input reverts to default parameters or 0. I doubt it's a bug but rather by design. Whether that's a good thing is another matter, but if each identifier with this behaviour gets reported as a bug separately there's gonna be a lot of reading to do on this forum.

This topic is similarily based.

Actually this will only happen (but perhaps doesn't in all cases) for identifer parameters that only accept numbers... So an identifer like $chan(#chan) / $chan(1) would not have the problem...

It has an aspect of $calc bug I suppose, $calc has other problems though.