Source managed bass management idiosyncrasies.
DEcoding in the source unit can have it can have it's drawbacks. I have a Denon DVD 1940-CI universal player that has SACD/DVD-A abilities. SACD, FWIW, needs to be decoded in the player and fed in 5.1 analog to the receivers "ext in" jacks since my receiver doesn't decode SACD.
In fact, I can't think of ANY receiver that does SACD internally.
Anyhow. it DOES play 5.1 MC SACD (good) but when setting up the speakers in the player, if ANY speaker is set to "large", the subwoofer doesn't play (bad). All speakers must be set to "small" to avail myself of the subwoofer.
Since I like to run my speakers full range AND use a sub, this is bad.
This follows through the DD/DTS as well. At least I can use a digital link to the receiver for that.