Contained Zombie Villages glitch outside containment and die in sunlight.

I built an elevated glass box and put 10 villagers in it (to use in a iron golem farm.) Due to no roof, a zombie got in there and now all my villagers are zombie villagers. I put a roof on the box to keep them from burning up while I gathered the resources to cure them.

I went to the nether to find a blaze rod. When I returned, several of the zombie villagers were outside the glass box on the ground, burning up in the sunlight.

I restored from a backup and the same thing happened again later and I hadn't gone into the nether. I can go to the nether and return and sometimes it doesn't happen, but it is frustrating to lose my progress because the zombie villagers glitch outside the box I built to keep them safe and I have to restore from a backup.