User has to login a second time when upgrading.

Hi There,
I'm just confirming this is how ProSites is meant to work with a sub-domain install.

1. User signs up and gets a free website by default. They may then choose to upgrade to whichever levels you define in Prosites.

2. User logs in to site, then they hit the "upgrade" button in the navbar or admin header.

3. The user is then re-directed to the parent site. Where they have to login again, (because its technically a different site)

I think this is a bad user experience, why should the have to login a second time?

So my question is:
1. Is there a way to allow users the ability to upgrade without having to login a second time? Can this be achieved with a sub-directory install? OR, is there another method or perhaps my install is broken?