i wonder what's different about my setup then. Do you have Geforce Experience installed? I don't have my program running now and i've got PCM on my receiver, and it switches to DD/DTS and back again correctly when playing videos, so on my PC at least, the bug is no longer there!
I have a GTX 660 connected to a Pioneer receiver, using 322.21 drivers and Geforce Experience 1.8.1, and i'm on Windows 8.1 x64
I also have a secondary sound card attached for my recon3d omega headset but it's only set as my default communication device
I'm actually building a new pc later this week, so it'll be interesting to see what occurs then!
I would love to hear from more people who use AVR Audio Guard, is the bug still there on your system?