1) You should not use Windows Live Messenger 9 if you're not an official MS Butterfly
2) It has been stated that Messenger Plus! is not fully compatible with WLM9 yet, since things will change and people aren't supposed to use WLM9 either.
3) The Idle status is what it is, another status. So not everybody who is Away is actually Idle. It is just that the Idle status in Messenger has the same name as the Away status. But both are different statusses.
see How many Idle statuses does WL Messenger have?
3b) The only thing that Plus! does in regards to this is changing the resource string of the idle status from "Away" to "Idle", so that there is a visual difference between people who have the away status (shown as "Away") and people who have the Idle status (now shown as "Idle"). That's all. So any misbehaviour of idle statusses vs. away statusses is Messenger's own doing.
4) Since Idle is just a status like any other status, you can set yourself to Idle with some
tricks. That doesn't mean:
a) You can't talk anymore to your contacts
b) The Idle status is automatically reset back
Conclussions:
Don't use WLM9 if you're not an official beta tester.
There is no bug at all concearning this, it all works as it should.
/ 
