I already solved it myself. For some reason, the internal filter was deactivated for Matroska files. I still don't know how that happened and why it was even worse for some files, but it doesn't really matter anymore...
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Without even changing a single setting, my setup suddenly started using Haali Media Splitter instead of the LAV Splitter it used before. I can't find any language and subtitle options in the Haali menu, so that would already be a big reason to go back to LAV. But there is a bigger problem: On some files that definitely worked just fine, I can't even get the video to play anymore (it can't find any subtitle and video streams, but the audio still works).

Why the hell did it switch to another splitter without me changing anything at all? And how can I go back to the old one?

If I knew how to reproduce it, I would have solved that problem myself because knowing why it doesn't work makes it pretty obvious how to fix it...

I've already reinstalled all of the programs related to SVP and it still doesn't work.

Thanks for telling me about LAV using windows registry though - that makes figuring out a solution a little easier.

I either don't understand what you're saying, or I'm on the wrong forum...

This is not a bug-report, but a desperate attempt of getting help. My problem is that they're not saved and after closing and reopening it looks like I've never changed anything.

After installing MPC-HC SVP on my new computer, the LAV Splitter doesn't keep its audio- and subtitle-selection-settings anymore. The videos with multiple Dubs and Subs should open with a certain audio- and subtitle-language.

Do I need to somehow activate LAV Splitter first, or what's the cause of this problem? It doesn't even change the language at all and even if I open it right after closing it all the settings are as if I didn't change a thing.

I'm talking about this window by the way, just in case it's not obvious