I don't remember this ever happening in the past, but now say for example i summon Durnehviir, then conjure a Daedra Lord, the Daedra Lord will overwrite Durnehviir and remove him, leaving me with a huge cooldown on dragon shouting and leaving me with nothing to show for it... Same goes for any other shouts that summon something...

Needless to say, this is balls.

Unless you have the summon 2 perk you can only have one summoned follower so the dragon goes. Try it the other way to see in the Daedra goes.

It does, needless to say this did not happen pre Dawnguard.

That's happened for a while, I think the nord hero shout does the same thing. Not really that big of a problem from my experience.

I could say the same thing for vampire eyes for beast races

I see what you did there, I suppose what I meant to say was that's not a new issue. It's been happening with summon shouts for a while now, I usually just use only one of them at a time in those cases. I would like to see it fixed however.