[Mosu]

mkvmerge 4.0.0 does NOT write default values in the headers anymore. Default values are a feature that the Matroska specifications have had since the beginning (2002). For example, the default value for the track language is "eng" (English). Therefore this value will not be written to the headers if its actual value is "eng".

Any player still having problems dealing with this should be fixed. Those are bugs in the reading application (player), not the in the writing application (mkvmerge).