Question about DK diseases on the HUD...

[ThaOne]

Ok, so yesterday I was in a CoS run on my 77 DK (unholy)..
Group setup:
DK Tank, blood DK, my unholy DK, ret pally and a druid healer...

Here is my question..
There would be times when I'd just refreshed the diseases (and they showed on the HUD), and one or all three would disappear from the HUD. Of course, this got to be very bothersome, as I only use IT, PS, BS, SS and pestilence (No Obliterate), and I have the pestilence glyph, so it refreshes diseases on current target as well...

I'm trying to figure out if this was a bug with the HUD/nUI or if there is a DK skill that removes other people's diseases as well... Such as Obliterate..
Or, is this a problem with nUI and instead of keeping my diseases showing when someone else used Obliterate (untalented)...

I greatly depend on the HUD's display of my personal debuffs on the target. Has anyone else had this issue, or can another (more experienced) DK fill me in here?

As a side note, the DK tank sucked.. using blood boil on the lil zombies as if it would do anything without a single disease on them (one hit kills them, obviously)...

TIA

edit: Regarding the DK tank.. Ok so BB does do a little damage, but obviously wasn't enough to keep them off the healer.