Why doesn't Team Explorer shows dll files in "Detected Changes"?

I have added two files to a folder that is under solution, but not in the solution tree (it is in a packages folder):

a.dll a.dll.txt

When I go to "Detected Changes" on Team Explorer - Pending Changes, in the list I see a.dll.txt but a.dll file is not there.

I did check all relevant .tfignore files to make sure .dlls are not excluded.

Question is: what is filtering out dll files from detected changes?