When using HDMI inputs Samsung "SHALL NOT PASS" HD AUDIO. It's annoying but true. You may have found a workaround but mixing some HDMI switch is going to be a mess.

If you want 5.1 the right way is to use a RECEIVER. All HDMI sources go there and the video goes on to the TV. For the reverse from TV to Receiver you can test with ARC but use Optical when that fails.

Nothing new going on here. Widely discussed. Not a bug.