Same. It seems the only way to stay /AFK is to already have your fingers on alt+tab as you hit enter on your "/afk" command, then alt+tab out of the window really fast. Either that or give up on the command altogether and just let the auto /afk system take you away after a while.

But neither solve the problem of someone coming back for a moment to check retainers or whatever and wanting to remain /AFK while they do that ~_~