Completely correct! Yes this could happen. If it keeps happening, then the 17th entry would cause the hash to be re-sized. Then again on the 33rd entry.
It sounds like Perl 5.8.3+ has made some improvements! Great!
For Perl versions less than that and even on Perl 5.8.3, I don't think that a user will know more than #buckets, #buckets used and #total entries (ie, user wouldn't know the max entries into a "bucket"), but given those 3 things, a user
can make some judgment call about increasing the hash table size and is able to do so.