DENYUSERPREFEENCES and ALLOWUSERPREFEENCES are mentioned in TWikiVariables
. Those are to avoid or limit user preferences messing up variables. If you set DENYUSERPREFEENCES "all", user preferences are totally ignored. However, it had the side effect of preventing
This is due to a bug in
Not many people are using DENYUSERPREFEENCES and ALLOWUSERPREFEENCES, the impact is small.