The current EE implementation ONLY supports exact match -- no prefix, no permutations.
It iterates using "nextValueAtKey()" with a key derived from the GROUP BY columns.
This function requires a key which matches exactly on all columns -- the key can not be expected to match the correct rows if it has more or fewer columns than the chosen index.
I don't think that this is trivial to change for 4.0.2.

I think we should ship this conservative support and define new tickets to later support these trickier operation modes:
   -- if no exact index found, fall back to use one index wider than the group key with an end filter for all min/max columns.
   -- if no exact or wider index found, fall back to use one index narrower than the group key with a post-filter for all min/max columns.
   -- in any case, allow each min/max column to specify an override index that covers (group bys, min_max_argument) to go directly to the next min/max value (this may already be a ticket?).