Amm... to me your answer kinds of blends everything together and it makes it hard for me to understand what you are trying to do.
What you call "the condition" is not a condition effecting what tmaxout() does internally.
I meant, if you don't want to set the maximized bit *every time* in tmaxyout() under which condition do you want to set it?
At the moment your are not using any condition in tmaxout() for toggling the maximize bit.

I took it from your previous post that you have checked via debug output and confirmed that tmaxout() is always called when you double click - just the result of what it does is every second call, is that correct or did I misunderstand?
If this is correct, then it means that the maximized bit was already set when tmaxout() was called the first time. (remember it toggles the state, so if it was set, it will unset it in the first time which would explain the behavior you see).