[SalesForce] Communities root URL redirect issue

I have an instance which has a Sites domain, call it "sites.force.com", and a Communities domain, call it "comm.force.com".

The instance has a single Community set up at a sub-folder, call it "/c1", so "comm.force.com/c1". We do NOT have a Community set up at the root ("/").

The problem that we're seeing is that when a user gets provisioned, they get an initial login email with the "set password" link that looks like

https://comm.force.com/c1/login?c=[long_token]

That works fine. But once a user hits that link and sets their initial password, if they attempt to re-open that original link from their email (as many users do), they get auto-redirected to

https://comm.force.com/index.jsp

Because there is no community at the root URL, they get the standard "under construction" screen.

Is this a platform bug, or is there a configuration fix for this I'm not aware of? If the redirect instead took the user to

https://comm.force.com/c1/index.jsp

(as I think it should in this case) everything would be fine.

I believe I could possibly provision an additional Community at "/" that just does a redirect, but that may have licensing/cost implications, as well as preventing us from provisioning a Community at that location in the future.

EDIT: this has been published as a Salesforce Known Issue, apparently slated for a Winter '15 fix. If it affects you, please click the "This Issue Affects me" button on that known issue page.