Here is the issue: The Infected open the doors that lead inside a house if they follow you. But if you are inside the house and close the doors (inside to inside) they seem to walk throught the walls. If you want to escape you have to open the closed doors.
Other people who i have talked to confirmed this issue.
This is a duplicate report and/or the developers are already aware of this bug/problem.
Please check the feedback tracker to see if an issue exists before creating a new one and instead vote the original one up so the developers can see it's a common problem. (Most of the most popular will be up top if ordered by Priority).
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A list of important bug/issues that the developers are already aware of can also be found on the DayZ Forums:
http://forums.dayzgame.com/index.php?/topic/153994-early-access-important-information-known-issues/
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Big update is set for the future to fix all the zombie problems, it's a LOT of work though.
Cheers