ZDoom

Ok, now I understand the technical limitations in place here, but the automap mode not changing right away doesn't feel like expected behavior. Therefore I would suggest that the console would print a message somewhere along the lines of "am_textured will be functional in the next level" when the setting is turned on. I think this would at least prevent possible user confusion on the textured mode not activating.

The textured automap requires GL nodes. If the level doesn't have them prebuilt, and the option is on, ZDoom will generate GL nodes with its built-in nodebuilder; but if the option is off it won't. There are therefore only two ways to address this: either always build GL nodes when they're missing (simple but maybe wasteful), or somehow make the engine build these nodes, if needed, while the map is being played if the option is turned on (I can't imagine this being simple).

Note that GZDoom shouldn't suffer from this since it always build GL nodes as it also requires them for rendering.

If a level is started with the textured automap turned off and it is then turned on during the level, it won't work and the automap visibly stays in the non-textured mode until a map change occurs.