Well, when I use the custom status, it all seems to work fine. However, for the '(Idle)' section you mention, when creating the status you need to add the 'Name Tag'.
e.g. : 'NAME'-'(CUSTOM STATUS NAME TAG)'-'(GENERAL STATUS)'
e.g.2 : Fred - Eating dinner - Away
With Plus! Live you can now also set your personal message to change as well as your status.
Also, it might be useful to know that you can set multiple auto-messages, which, in my opinion, are GREAT!
What these do is that when someone IM's you, the auto-message (a-m) will appear. Then, if you have set multiple a-m's, if they type somthing else, then a different message will appear.
Now, to do this...
[list=1]
[*]In the auto-message box, type your 1st a-m
[*]Then click the ENTER button on the keyboard
[*]Now type a # sign
[*]Now continue, and type your second a-m
[*]You can continue to do this
[/list]
Here's an example:
I'm not available
#I said I'm not available
# Hello! Can't u read? I said I'M NOT AVAILABLE!!!
# OH! I give up! 
Also, I think, but I'm not possitive, that if u include a command such as '/away' in your a-m, it will change your staus to a different staus (in this case, away).
So, I hope this has answered your question and helped to improve your messaging experience!
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RE: Set message when idle?