I’ve carried this type flashlight for several years now, everyday at work I use it. This morning was seeing a patient and I use it to look in mouth/throat. I noticed the plunger button was swollen like a ballon but light still worked. Finished seeing patient and back to my desk to unscrew the cap and it makes a pressure release pop. Batteries looked good, normal Duracell batteries, nothing special. Tossed the batteries and put light back in bag empty. Anyone ever have an issue like this? Got me thinking and worried a bit as I carry this in right front pocket, metal tubed flashlight would be a problem if it structurally failed. Probably leave a mark.

In answering your question, "No I haven't had anything like you had happen with the pressure in the light."
First thought would be the batteries going bad, and gases from them.

I'd write/email Stream light and tell them the issue, to see if they have an answer.

God Bless,
David B.

Call Streamlight on Monday and see what they have to say.

I carry a Streamlight Microstream USB on me everyday

It seems like Duracell (regular and.Ultimate) start corroding faster in my game cameras and flashlights, than the Energizer or other equivalents. Batteries are left in those items long term more often, for me, so that’s the only reason I’ve noticed when changing out batteries. I would think gasses would be emitted before the corrosion is visible and if the pressure cap has an o-ring the battery tube is sealed and the pressure build-up would make sense.