Weird backslash on expand-word on braces

[Mikael Magnusson <mikachu@xxxxxxxxx>]

{$((1))..$((3))}

Pressing tab pretty much anywhere except after the final } works and
gives {1..3} as expected, but at the final } it gives {1..3\}. Happens
in zsh -f with no compinit done too.

-- 
Mikael Magnusson

If anyone is wondering what I'm doing, I was experimenting with a
braceccl like function that works for multibyte,
% for a ({$(( ##a ))..$(( ##z ))}) { echo -n ${(#)a} }
abcdefghijklmnopqrstuvwxyz
% for a ({$(( ##â ))..$(( ##â ))}) { echo -n ${(#)a} }
ââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââââ

Just wanted to check that you can have $(()) inside {} and pressed tab.