Digging into the code shows that this behaviour is clearly written their[1]. It it only triggerable by either external auth or access log formats which includes parts of headers with delimiters.
Bastian [1]: src/HttpHeaderTools.c:239-283 -- Without facts, the decision cannot be made logically. You must rely on your human intuition. -- Spock, "Assignment: Earth", stardate unknown -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org