Displaying debuffs is broken for me.
I had the same problem but I figured out a solution: http://www.wowace.com/forums/index.php?topic=1592.msg99917#msg99917
If you don't fear editing a single line in the TinyTip source file you can easily fix the debuff problem.
It's in line 183 of file "TinyTipExtras\TinyTipIcons.lua". The old code line is missing a comma, so updating the old line
_,_tmp,tmp2 = _G.UnitDebuff(unit, i, flag ~= 1)
_,_,tmp,tmp2 = _G.UnitDebuff(unit, i, flag ~= 1)
solves the problem and you can see the debuffs again. :)