Rationale:

The rationale is that it doesn't matter, and you can't check: the lock types may be different, or the same and user-defined, so the implementation must provide internal synchronization anyway.

[ 2010-02-12 Moved to Tentatively NAD after 5 positive votes on c++std-lib. Rationale added below. ]

For condition_variable_any, must all lock arguments to concurrent wait calls "match" in some way, similar to the requirement in [thread.condition.condvar] that lock.mutex() returns the same value for each of the lock arguments supplied by all concurrently waiting threads (via wait or timed_wait)?