Zombie Crawler spawn

[Tankenstein]

I am wondering if anyone else has zombie crawlers spawing inside their base? Ithas happenend twice to me in the past 12 hours. I have a two story base and have a sleeping bag on both floors, as I read somewhere Zeds don't spawn within a certain distance of the sleeping bag..?
The spawning is happening on the ground floor not on the 2nd floor.

[Jᴧgᴧ]

Crawlers used to walk through walls a few builds ago, are you sure they are spawning inside or perhaps they are crawling in?

[Tankenstein]

I am sure they are spawing inside the base. I have created a foolproof base as an experiment. The house I am using is surrounded by bedrock wall 15 blocks high with a overhang to block spider zombies. And I went 6 blocks down with the bedrock walls and no Zeds are digging under to get in. And crawlers are the only spawns inside the base.