I can't say for sure, so i'll ask it as a question
I have an @window open with a menu and in the menu is /window -c @window
which closes it fine, but i added an fkey alias

alias f3 { /window -c @window }

and that won't close it, any reason why?

Worked here. Maybe you have another
F3 alias that is being loaded first?

//echo -a $isalias(F3).fname

alias F3 window -c @test
menu @test {
Close (F3):window -c @test
}

~ Edit ~
I Don't know why you deleted your post but...

Using v6.17 but I just tried it on v6.16 and it worked fine
there too. Maybe it's a difference in the window properties,
but I can't see why, I just used /window @test with no
parameters.