Ever tried to morph an unit after you gave it an ability via UnitAddAbility? Well, I just did yesterday when working for Blade's spell contest. I simply froze when I realized that the abilities would disappear when unit morphed, and would not reappear when switching back to original form. The bug occurs for spells like Bear Form, Storm Crow Form, Tinker ultimate and Submerge. Even Metamorphosis is affected by this bug.
This means that all buff spells which add abilities to the unit are buggy if the unit can morph. I'm not sure if weaadar's system (hope I didn't mispell his name) does not also add abilities permanently to the unit, in order to increse different stats. For mana and life I would suggest sticking to blade's solution which does not permanently add an ability (just for a slight second, making it immune to this bug).
I don't know if you are familiar with this problem, but I thought I should mention it in case you didn't. :)
~Daelin | 
JASS: