During my recent play throughs of Doom and Hexen games I encountered some problems:
1. Saving on small platforms. Observed in both Doom and Hexen. If you save your game standing on a small sector (size comparable to player's) then upon loading that save you may find yourself immediately falling right through that platform. I encountered this in Ultimate Doom E4M2 on some stairs leading to exit area with Cyberdemon (the ones blocked by blue key pillar) and in Hexen in Shadow Wood in a cave with moving floor parts.
2. Some moving objects in Hexen do save their parameters properly. Example: in Griffin Chapel (Hub 3) there is a room with moving walls where you are required to press four switches while avoiding those walls. If you save after the walls started to move and then load that save, you find that walls move in a very strange manner, misplaced. I might be wrong but it looks like their positions when you saved became their new origin point.
3. JDRP Specter rendering problem. After you start the level with Specters they render with black tint as they should:
However if you save and then load the game, the black tint is gone and they are rendered simply as pink demons but transparent:
4. This one I encountered only once and it was gone all by itself after a couple of minutes:
As you can see model surfaces are all turned inside out.