The rules on the wiki don't take into account a possible bug in 1.5. The tests done in How do I construct a safe sleeping area in 1.5 version?How do I construct a safe sleeping area in 1.5 version? suggest that the amount of flat space in front of and/or behind the door you use could be the culprit. Making sure there were 4 blocks both in front of and behind my doors did fix the problem in one of my bases, although there appear to be other circumstances that also work.