Ok, now I believe that those differences between Ultimate mode, normal mode and filters are just another bug.
Hear me out here.
Here are my findings:
When you switch from normal to Ultimate you lose some amount of clarity. But, and here comes the strange part: except for the D5 filter. If I have this one chosen (and this one only) I hear no difference while switching between normal and Ultimate.
So I can easily tell apart D5 from any other filter while having Ultimate on.
This applies to Mango app and os as well as other apps I tried.
Funnily enough Neutron is the exception but only in oversampling mode. How about that?