Converting to webm (VP8) in super low quality

Converting files (mp4) to webm (VP8) seems to be broken for a while. The output video quality is potato-like. Changing the bitrate doesn't seem to work properly. The output filesize is always the same.

My output settings are: stop-time=10.000 Disabled Audiocodec All other settings are default

I tried different versions because I knew, in earlier versions there were no problems. V3.0.1 win64 bit seems to work properly. In v3.0.5 win64 and bigger it doesn't work (didn't check the versions in between).

Unfortunately I'm not familiar with debugging VLC so if you need some further information, you need to tell me how to get them.