Placing doors below you makes you be 'inside' them

I was making a house when I accidentally broke a door instead of opening it (still can't get the han of the left- click-hit and right-click-place/use) and, when I placed it on myself (still can't remember why I did that), I found out than I was inside it!
First thing for moderators: this is not a dupe of a bug when you close a door on yourself, you go inside it. No, this is about placing it and directly being inside it.

Giorgio