Comment 3 for bug 1451184

memcached_server_response_count(ptr) returns 0 when ptr is NULL or ptr->cursor_active is NULL. Decrementing this and assigning to a uint32_t produces 2^32-1, so the error check if (no_msg > 0) only fails if ptr->cursor_active == 1. I suspect the right answer is to not use uint32_t here (before it was uint32_t it was int; not sure why it was converted to unsigned) and instead use int32_t. That change is here:

http://bazaar.launchpad.net/~tangent-trunk/libmemcached/1.2/revision/509/libmemcached/memcached_purge.c

For what it's worth, I've seen this bug tickled when calling set with a key containing a newline (\n) from PHP 5.5's Memcached class. The Memcached server doesn't like that (seems to be interpreting the second line as a new command) and errors out -- eventually triggering this loop as it attempts to unwind from the error.