This was noticed during the review on MDL-80746.

Action bar filters (groups, users, initials) used in both the gradebook and in assignment submissions page. Currently, they behave the same way, so consistency between these pages isn't a concern right now. What is a concern is the way the filters interact with one another on the page, and this can change depending on the order in which they are applied., as you'll see below.

For example, with respect to ordering:
a) if I search first, then select a group, the group selection reset/unsets the user search.
b) if I search first, then select an initial letter, this doesn't unset the user search.
This highlights a difference between the group and initials filter.

We also need to consider the UX of the reverse situations: where we set a group/initials filter first, then search for a user. Right now, the group/initials filter value is kept and is additive with user search. Of course this is strange since it works a different way when done the other way around (user search first, as above).