The complaint in bug #14927 that heap_drop_with_catalog is not bothering to check for SearchSysCache lookup failure (in code evidently newly added for the partition feature) seems to me to be only scratching the surface of what's wrong with that code. In particular, I do not understand how it can possibly be deadlock-free to be trying to grab AccessExclusiveLock on a partition's parent table when we already have such a lock on the partition. Which we do, or at least had better, long before we get to heap_drop_with_catalog.
regards, tom lane