the context of expansion for output redirection

[Lewis Hyatt]

Hello-

I was somewhat surprised to see the following behavior (this is 3.1.17):

$ x=0; /bin/echo > /tmp/$((++x)); echo $x
0
$ x=0; echo > /tmp/$((++x)); echo $x
1

I guess in the first case the expansion of $((++x)) is taking place after
forking, whereas in the second case there is no forked process so the expansion
happens in the context of the current shell. I would have thought that both
cases would output "1", though. Is this expected or documented anywhere? Thanks
very much.

-Lewis