Can you try searching for "grid" again? Should be fixed.
I *think* that in this case it is treating each side of the query as a sub-clause and perhaps the mm rules aren't enforced for sets of sub-clauses. I've tried several things to force the correct behavior to no avail. For now I will need to move on to another item, but I'll keep the internal bug report Mitch filed for this open for further research. Meanwhile explicitly using AND between the clauses does coerce the desired behavior.
Thank you for all the useful feedback you have provided us about the search implementation, we are listening!