Update: With the new build HD works well for most of the channels now. The entire transponder with "Tagesschau 24 HD" and "ONE HD" doesn't work at all (is kinda dead). Deleting these channels and doing a search for new channels didn't solve it.
I have the same issue with Netstream4sat that every HD chanel is in low-res. I opened a ticket in January, but got no feedback. Would like to test this Beta build 8525. Hope it will be released soon.