HTC One S vibration keeps getting turned on for normal profile
In my ICS (on LG Swift hardware) the switch to "ring" profile occured on every answered call during daytime. Somebody else at Polish LG forum complained about switching to "quiet" at night. 

SOLVED: After some reading and a simple experiment I found that it is the system app to switch profiles for the nighttime (settings->sounds->"silence time" in my LG). This is a buggy app: after any event requiring sound on - like answered call or so -- it switches to the scheduled profile, even if it was overriden manually.

To make clear: I have "nighttime" quiet setting, so after manual switch to "loud", upon first call it automatically returns to "quiet". In the daytime, when quietened manually, after a first call it returns to "loud".

Switching this option off helps.

P.S. I have read about problems with tasker after upgrade - maybe it is some more general bug (or feature making some apps incompatible)