Thx to moeller0 for the heads up about this thread. I work at Comcast and am working on AQM and low latency stuff (among other topics). As part of that work I've been mucking around with DSCP values and WMM to prep for dual queue networking. I noticed the post saying packets hit the WLAN marked CS1 and that might drop packets into AC_BK. I see the same marking on my WLAN, though upstream packets to my AP are marked CS0.
Anyway - issue noted & being discussed internally.