With the 1.3.0 upgrade, the findOne test within PHPLIB began triggering this assertion failure in libmongoc:

src/libmongoc/src/mongoc/mongoc-cursor.c:52 _mongoc_n_return(): precondition failed: remaining > 0

Dumping the Query object in the PHP driver reported int(4294967295) as the limit (largest possible 32-bit int), which jives with libmongoc using a uint32_t for the cursor limit and PHPLIB specifying -1 for its FindOne limit. IIRC, -1 and 1 are both handled the same by the server (the cursor is immediately closed), so it's a trivial fix in PHPLIB to use 1 instead of -1.