Skybox visible only
When one loads a hires skybox and plays the game, for a quite a few builds now, looking at the skybox makes everything disappear but the skybox; getting a full screen skybox picture with nothing else visible, no level geometry, no hud, nothing. Managing to turn yourself away from the open sky brings the hud and the level back, and turning back toward skybox makes everything but the skybox disappear again.
Having no hi-res skybox texture loaded as a mod, and the game runs normally without this problem.
This is happens in both Doom and Doom 2.