Is there a way to deactivate the 'MySites' button from admin bar for end-users?

Hi there
I am developing a basic pro-sites setup just like Edublogs and when testing have found something peculiar and I'm not sure if it's meant to work this way.

If a network user (not superuser, just a site admin) logs into their own wp site - and then clicks the upgrade button - they will be taken to an upgrade page on the host wp site. So far, so good.

Their admin bar will still be showing at this point, if they then hit the 'My Sites' button on the top left, rather than seeing a page with just their sites listed, they will get an error message saying they cannot access the host site's 'sites' page as they do not have the appropriate permissions. I'm assuming this is because they are now on the host site.

This isn't really a good experience for the end-user. After they login, they should only be logged in to their site from then onwards, and any links in the admin bar should only link to their site. What If I hit the 'Upgrade' button - and then change my mind. In an effort to go back I hit the 'My sites' button, thinking this will give me access to any of my sites - only to find that I get an error message saying I don't have permission for the host site...

Any workarounds for this?