To recreate: Open a map and place a large amount of redstone lamps in a big square.
Note that the area covered by redstone lamps now appears on the map with the same color as orange terracotta.

Expected behavior: Redstone lamps do not show up on the map.

My understanding is that this was changed because someone had it marked as a bug that redstone lamps are transparent on maps. I would make the case that this should be reverted to the previous behavior and not be put into full release.

The redstone lamp was a very unique block for maps, in that it's the only transparent block that blocks light, and can be powered through. This makes it very useful for map display tech, chiefly, it allows a roof to be built above the map display to prevent undue light updates (lots of pistons on map displays). There are years of tech built on top of redstone lamps being transparent, and there's no alternative transparent map block that can do what it does.

Unless a new or different block(s) could inherit the map features of redstone lamps, this change will be very challenging for the field of map display tech. Alternatively, a middle ground that would actually open up new display tech would be to make it so that when the lamp is on, it shows on the map, but when it's off its transparent.

Thanks