Indeed I do. It's because your minions remain at the higher level otherwise which is open to massive exploits. Apparently they can't lower the levels of spawned mobs dynamically.
One could ask why not given the fact that the only truely new AT in villains relied on Henchmen and the prevelence of Sidekicking & Lackying ingame but you probably wouldn't get an answer.
You do get a short period of time to redress the range between you and your lackey before your henchman fall over.
And as others have siad it is to ensure your henchmen are the correct level for your current combat level. No controlling L40 Assautl Bots while only L28 
Then I take it this is also happeing in coh then for phantasm, fire imps, dark pet, ice and stone pets then?
Yep as far as I know.
Generally it doesn't matter as much though, they aren't as reliant on henchies as MMs are.
Yes, it was like that long before MMs entered the game.
I really should do something about this signature.
If the Boss/Lackey is moving out of range enough times for it to be that inhibiting, surely the problem is with the partnership and not the game?
That said, would be nice if they could dynamically change the level of the pets, but I can't see this happening.
Anyone understand why the devs decided that if your lackey goes afk, or runs in a middle of a fight that your henchmen just die? In my view, this is totaly usless and leaves me completely defenceless.