bedrock not unbreakable

I was using the vanilla technique to trap wither boss in the nether ceiling to and kill it, but the explosion that the wither boss does when you spawn it blew up the bedrock (3x3 area). All his projectiles was breaking the bedrock as well. Any explosion, as tnt, also breaks.

Suggestion: Make the bedrock be spawn proof as the vanilla one is, so mobs cant spawn on top of the nether ceiling

Modpack: the new frontier 1.11.2 version 25.1 Mod version BedrockBGone-1.11.2-3.0.4