Game sometimes fails to render space behind doors/platforms for a tick when opening

[aaronfreed]

It only ever happens for a tick, and it only happens in some setups, but it’s pretty noticeable. I can usually predict some setups that will cause it (split doors that line up exactly with adjoining polygons are especially likely to cause it). It’s been this way since the vanilla games; several places in “Post Naval Trauma” and “Foe Hammer” cause it. Here’s a video of the glitch in action:

door.flicker.thing.mp4

And here’s a map you can examine for yourself:

dumb split door test.zip