Matt
This style of HVAC box was developed by Denso to be much more compact than traditional "blend Door" style HVAC boxes. It doesn't need the physical size to allow for opening and closing doors inside.
The new Denso style door is more like a cavity sliding door than a swinging one.
The door itself is made from clear plastic, very much like a piece of laminated paper without any paper inside.
There is a fine stainless mesh screen that supports the clear door from bellowing inside the box, caused by air pressure from the blower fan.
These doors are operated by a cable sub assembly that rolls or winds the doors through their range of operation. These cable sub assemblies fail very frequently and no longer operate the doors correctly. They are like 3 very fine wires inside a moulded plastic outer, with a dial on each end. One dial connects directly to the sliding door on the HVAC box, the other to the control knob behind the dashboard. I've replaced countless on Yaris's and other Toyotas.
Ref fig 87-15
I have replaced many heater cores in 2005 -2015 Hilux's, but never seen and issue with the actual sliding door arrangement. Thanks for the heads up, I'll keep a keen eye out for this issue.