http://curl.haxx.se/libcurl/c/libcurl-share.html says:
You tell the shared object what data you want it to share by using curl_share_setopt(3). Currently you can only share DNS and/or COOKIE data.
But if you click the link and go to http://curl.haxx.se/libcurl/c/curl_share_setopt.html, it also lists CURL_LOCK_DATA_SSL_SESSION.
I suggest removing, "Currently you can only share DNS and/or COOKIE data," from the summary.
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/