I ran into this when I was testing a FireTV and Flirc dongle on many apps and a few with Roku in the past even before the Roku firmware update. I have read that it is a common problem with universal remotes. They have to accommodate so many devices that they all send multiple signals for a button tap which is why it is adjustable on the better remotes.
You may have even noticed in the MyHarmony app screens that I reference above it states to use that setting specifically if your having problems with the up/down channel and volume keys.
I'm sure Tablo could make it work with Harmony remotes with 3 signals sent but could that possibly make another brand universal remote not work at all on the up/down keys? IMO this is why it is adjustable on the remote itself and not just a "work around".
At any rate, I hope my post helps.