There has been an update in http://www.rememberthemilk.com/forums/help/4006/ :
emily (Remember The Milk) says:
Okay, it turns out we're not using any class names (so that method
won't work to identify our fields), but sewpafly could ignore any
fields that are inside of a div with an id 'remember-the-milk' or a
class of 'rtm-task-card-container'. Hope this helps.
I haven't used those extensions a lot these days, should there have
been an improvement, I couldn't have noticed it.
Patrick
Give this one a shot:
http://groups.google.com/group/gmail-power-users/web/modifiedgmailmacrosv20_rtm.user.js
sewpafly