Because the trigger is executed for each character, not once for the update (i think; thats what was happening with me anyway). So it would be difficult to clear the groups before processing.
I didnt look that hard into it to be honest
EDIT:
Just noticed this in the SDK:
Available variables
- $wowdb = roster's db layer
- $member_id = character id from the database ( ex. 24 )
- $member_name = character's name ( ex. 'Jonny Grey' )
- $roster_conf = The entire roster config array
- $mode = when you want to run the trigger
= 'char_pre' - before character updates
= 'char' - during a character update
= 'char_post' - after character updates
= 'guild_pre' - before guild updates
= 'guild' - during a guild update
= 'guild_post' - after guild updates
I will code the trigger with a guild_post.... monday maybe, busy this weekend