Subsite styling gets reset every time I add a user

I have a need for users to have roles on more than one site. Generally, I create the user for the main site, and then Edit the subsites I want them to have roles on and add them with the relevant role.

The problem with doing this is that it immediately resets all of the theme options to their defaults for the subsite. I think this happens because the chosen theme is a site option, and when you hit Update Options in the site users section of the Edit Site screen it updates ALL of the options and not just the site users.

I am using the 2010 Weaver theme, if it makes a difference. If I need to post this issue at the 2010 Weaver forum instead, do say so.

Many thanks to anyone who has suggestions.