MediaCoder

I don't know exactly what would cause that without having access to the files that fail but try preventing tags from being carried over by clicking on the Text tab and unchecking Transfer Tags.

I found it searching for video converters on Google. I knew about MediaCoder for some time after I found out about it and used it occasionally, but I didn't become an active user until Avisynth support was included and perfected (I used mainly MeGUI before then due to its use of Avisynth which suppo...

It is possible only under the Full Edition. The only settings you need to set with the full edition are Copy Audio under the Audio tab and Matroska container with MKVMerge as the multiplexer. It will automatically output .mka with copied audio (not re-encoded) as the result.