Had opportunity to play .61 experimental. In both days, infected have been IMHO dynamicaly spawned right with me in house - one was even closed.
Had this in alone house in middle of nowhere (north from Nadezdino) and in new oppened military baracks in Veresnik
Please check:
https://www.youtube.com/watch?v=ZDUAzpLhN0I from 11:00
https://www.youtube.com/watch?v=-sSkoI3XsXQ from beginning (specialy after 0:30 - you could see the hall was infected free as I have locked both infected in room)
I do not thing this must be a bug, but should be something to look at.