I have rooms built for villagers where I'll trade with them. I lure zombie villagers inside then cure them, that way there's little to no hassle when linking the villager to their workstation and bed. These rooms are almost fully enclosed. The only openings are the window which allows me to click on the villager to trade with them and a hole in the ceiling where the zombie villager initially falls to be trapped. But I always fill the hole in ceiling before going down to ground level to throw the Splash Potion of Weakness. Yet if the zombie doesn't finished curing before dawn, the sunlight still somehow kills them despite them being in their own little room with a fully filled in ceiling above them. I know light can leak in through the sides, but then again I've watched countless undead mobs stand under tree leaves out in the clear wide open in broad daylight without taking any damage at all, let alone dying. So either the part about zombie villagers dying by daytime while inside enclosed rooms is the bug or the part about undead mobs somehow surviving under tree leaves is the bug. The game has wasted soooo much of my gold (used to make the golden apple which is required for curing zombies) due to this bug.