Why does the AC3 core needs to be separated from TrueHD when added to MKV?

[zeropc]

can someone please answer this properly and is there a way to turn this option off?

sure, some might find this useful. but you can also run into issues do to the separation.

[sneaker_ger]

https://gitlab.com/mbunkus/mkvtoolnix/wikis/TrueHD-and-AC-3