The following %IF works fine on 1.1.4, fails on trunk.

%IF{"$ WIKINAME!='WikiGuest' and $USERNAME not ingroup 'AdminGroup' and '%REGISTRATIONGROUPTYPE%' = 'automatic' and not defined 'REGISTRATIONGROUPS'" then="<blockquote><span class=\"foswikiAlert\"> *Caution!* Registering a user while logged in will add the new user to all groups you have permission to change.</span> REGISTRATIONGROUPTYPE is set to =automatic=, and no groups are set in REGISTRATIONGROUPS. </blockquote>"}%

Fixing it by moving the not outside of the ingroup comparison - thanks pharvey

%IF{"($WIKINAME!='WikiGuest') and  (not ($USERNAME ingroup 'AdminGroup')) and ('%REGISTRATIONGROUPTYPE%' = 'automatic') and (not defined 'REGISTRATIONGROUPS')" then="<blockquote><span class=\"foswikiAlert\"> *Caution!* Registering a user while logged in will add the new user to all groups you have permission to change.</span> REGISTRATIONGROUPTYPE is set to =automatic=, and no groups are set in REGISTRATIONGROUPS. </blockquote>"}%

Test:

No parenthesis

else clause

With parenthesis

else clause

-- GeorgeClark - 30 Oct 2011