List import aliases not working?

I was just informed in my support case that this is new, expected behavior:

"Upon research I was able to find that Marketo will choose IGNORE for all fields that are blocked from list import updates. This is because the field will not be updated from the import so there's no need to map. This is expected behavior if the fields are blocked from updates."

So if a field is set to be blocked from updates by list imports, it won't automap when doing the list import. Rendering list import aliases useless for those fields.
This makes absolutely no sense to me. The purpose of blocking a field from updates is to prevent updates, not prevent the field from being written to in the first place. If the goal is to prevent the field from being written to entirely, then there should be a separate option in Field Management called "Block Entirely" or something like that. Don't break the good functionality that's been working for years on a whim!

I had trained our users on how to do list imports themselves, but now that they'll have to manually map our tracking fields, it further complicates their process and makes mistakes more likely. I'm sure people will soon be asking me "Where's Lead Source? I only see Person Source", etc.
Fields which were set to ignore updates were already underlined in green, making it clear which ones they are. Please restore the previous functionality!

We are having the same experience as well. I hope this is fixed quickly as it adds a lot of extra time to the process.

I am pushing back on Marketo Support's response that this is "expected behavior". I have a strong feeling that someone screwed up, this is actually a bug, and that someone mid-level in the company is writing it off as "expected behavior" because they don't want to deal with it. Or worse, it really was an intentional change, and just a very misinformed one without any user testing. Please prove me wrong Marketo!

Update here: I managed to get this reported as a bug, and was told a patch would be deployed with the June release. However, it looks like the automapping only happens now for the right-most column that was blocked from updates, in the below example "Opt-In Implicit."

I've reopened my support case. I'm guessing whoever wrote the patch was only testing with one field that was blocked from updates...

Update: they told me they had to roll back the last one and a fix is scheduled for August.