Yes, one major issue of this router is the IP QoS. Doesn't seems working. Well, go browse through several TP link forum and I've flood them with this question (We're not the only one worldwide). If you're wondering, there's a latest firmware that overcome this issue, but certainly can't get it work with Unifi. Here's the list of firmware I've tried.

1) TL-WR841HP_V1_140214(Unifi&Maxis Fiber) - stock, no issue just have problem with IP QoS
2) wr841hpv1_en_3_15_2_up_boot(150519) - from tplink website, got issue with Unifi
3) wr841hpv1_en_3_15_2_up_boot(141208)_beta - from support (email), got issue in setting up unifi (this is the one that solve the bandwidth control issue) at least user's from other country, not using crappy unifi ofc
4) wr841hpv1_en_3_15_2_up_boot(141116) - from tplink.my website, crappy firmware that cause severe hypptv stuttering and wifi not working on the next day

Despite good coverage, I tend to get major hiccup when pinging the router, may go p to 1k ms sometimes.
Contacted the tp link support and ask she me to gather this and that data. FGS, got get us a latest firmware that has IP QoS working properly and compatible with unifi!!

damn dulan, now like experimental router pulak. anyone have problem on the button of the stock firmware interface? it kept shifting to the left when u hover over it right?

BTW, the toll free number not working, isn't it? I couldn't reach them verbally.