Esplanade theme conflict with s2member plugin

I’m using the (lovely!) esplanade theme and have recently started looking into the s2members plugin for user registration and management.

However, the s2member admin pages appear to be incompatible with the esplanade theme – displaying the page as one long list of information rather than broken up into tabs (as is shown on other themes such as twenty eleven, etc. This not only looks wrong, but also prevents me from setting up custom field values et for the registration screens.

Disabling all plugins makes no difference. Only switching to a different theme worked.

I’m very reluctant to switch themes now because the site is in use and our users really like the design.

Any help would be gratefully received.