Today I rediscovered this more than five year old solution from Buchel:
"If you have problems with slightly blurred titles in an HD project and you are shure you have set all settings correct (media creation and timeline quality) I have a solution for you.
Open the Console and Type: "HDTitleFilter"
This toggles the title "anti-alias-downscale" filter to off and your new created titles get crisp. You already have washy titles? Just recreate them. This is also for imported graphics with alpha. (Matte Keys)"
See the complete thread here.
I did a quick test and was surprised: This is still valid in 2017 with MC version 8.9.3
Is there any reasonable explanation why this filter is ON by default?