Alas, yes - the easiest fix is to use the command /releasepets and then you can resummon. You can also try exiting and reentering the instance.
Personally I just dismiss my henches at the end of each mission and resummon on entry to the next to avoid this bug. Also means I don't trail henches across the zone 
Yeah, this bug has been around for months now. It doesn't happen all of the time though, but now I've gotten into the habbit of checking to make sure my pets can move by using the goto command ("/petcom_all Goto") at the beginning of each mission. If they don't respond, I just /releasepets and resummon.
There have been many times where I start a fight only to find out my pets aren't there and of course I get face planted. I wish the dev's would get this fixed soon, because it's getting very annoying.
So several times over the past few days I have encountered a bug, where I zone in with my pets to a map, and the pets will not move. They respond verbally to commands, but they sit at the entrance to a zone or map and don't move. I can't dismiss them unless I go to the original zone or exit the map.
This bug has made participating with fast-moving teams and/or SFs almost impossible.
I'm assuming that this is a known bug, but is there a way around it? Did I miss a thread on this?
Thanks in advance.
Ideally, the tank will die precisely as everyone else starts fighting, allowing aggro to be spread evenly among the blaster. -seebs, "How to Suck at CoH/CoV" Guide