Invincible Crafting Table Question

I think this was mentioned in book one, but wasn't it the case that one of the crafting tables he used were 100% invincible to damage, and he noticed it and then thought "Good to know but I don't want to test it any further in case it's a bug that they fix"

Did that ever come up where he used that as an exploit? If not, do you think that may be used?