I have the same problem, and also did not have it with plus 2..
But perhaps a suggestion for the next version / update of plus:
an option to chose whether you want your automatic status change to occur when 'online' only, or to occur no matter what your current status is.
Because i also find it real annoying when it changes my status when i'm already in a (personalised) away. I only want it to work when i walk away and forget to set myself to away, or when my connection is bad, and messenger has to sign in again (and then sets my status to online again)
And i saw that there is some kind of a solution for this problem, but i don't really understand it, and i'd rather just use the options in plus.