new (self) dispel mechanics

[Donruss]

I read the other thread. I still have no idea how dispel works. Daldaen's post was useful but I am not dealing with spell casting mobs. I have a few questions about the new self dispelling mechanics.

When I use cancel magic it is now canceling a random buff sometimes, but sometimes it works as I intended it too. I am using the spell cancel magic (low lvl) so shouldn't that only put my first slot buff at risk?

Example, I root a bat and then charm it. does cancel magic now have a chance to break charm instead of root?

Another example is the necro heal. Why is cancel magic not getting that when it is in the top spot sometimes?

I understand mob dispell is super crazy now, but i imagine they are casting annul magic or some higher lvl version that should jeopardize more than just the top slot? Shouldn't the lvl1 dispel only attempt to take away the first buff? If not, how many "junk" buffs do I need before my important ones are safe? 4? 5?