Except it's not an "error", it's simply a truncation. Errors usually mean "something unrecoverable happened"-- in this case, nothing really went wrong, the table was in fact created, it's just only using 256 characters of your input-- you don't need an error to know this will happen (documentation would be nice though). This works the same way the IRC server will accept a long /nick command without any errors but silently truncate it. If that is acceptable behaviour, I don't see why this is not.
I think you just need to be aware that your table names will have a limit of 256 chars and it's up to you to make sure you're under the limit otherwise expect your name to be truncated. The truncation happens across all hash table commands, so it should never affect any scripts unless you had 2 table names with the same first 256 characters, but raising an $error would not fix that problem-- you'd need better names.
All that really needs to happen is to have this documented.
