Air Conditioning, closed vent turns on automatically.
 

Not sure if this is the right section, but it's in-car electronics?

But I have the circulate internal button for the vents randomly turning itself on. I have the GTS model with dual climate control, so not sure if it's some passive setting I'm not aware of.

Anyone have that issue?

My BRZ does the same. Turn off the auto setting for climate control and circulation will remain as you left it. Drawback is that you will have to adjust the fan level to what you want all the time. I normally leave mine to what I like for air circulation so it's not a bother at all. :-)

Hope that helps.

So even when the climate control is all off, you get it switching that feature on by itself?

Thx for the feedback.

Review of the manual shows that this is designed to help control humidity. It turns recirc on and off as it sees fit.

I've tried turning off AUTO, having it set to free air. Turned off the Air COn. Then have it switch back on and it's set to re-circulation of air. It's a little annoying as it seems to do this while away and thus car gets hotter than it should as the vents aren't open.

I'm at a loss.

Without the AC running it will try to control the temperature inside the vehicle. Sometimes turning on the re-circulation allows it to do so easier. My Rav4 does this also. It's a "feature" of Toyota climate control. I've gotten used to it having had the Rav4 since 2007. Every time you start the vehicle you will have to adjust the re-circulation setting if the temperature is different enough outside to what you want inside.

Side note: The only climate control in a car I have owned that made sense was in my old RSX.