curl documentation states
--stderr <file>
Redirect all writes to stderr to the specified file instead. If
the file name is a plain '-', it is instead written to stdout.
This option has no point when you're using a shell with decent
redirecting capabilities.
The part
"This option has no point when you're using a shell with decent redirecting capabilities"
Is not exactly right (and could be removed): example
$ /usr/bin/time curl --stderr curr_out ... 2>time_out
Thanks for the report, this problem is now fixed in the git repository.
To try it out, you either checkout/update your git clone: http://curl.haxx.se/source.html
or you try tomorrow's daily snapshot: http://curl.haxx.se/snapshots/