Free membership level and "Premium" membership level conflict

Hello - we've been having a weird problem with Memberships. We have three access levels, 1) Visitors/Strangers 2) Free and 3) Premium (aka "0bserver" level).

The Free membership level allows people to register a username and make purchases from our WooCommerce powered store. The Premium/0bserver level is a paid access level which grants people access to protected content.

If someone has a Free subscription plan with us and then buys a Premium/0bserver membership, the two will co-exist simoltaneously and the buyer won't be able to access the premium content until I manually go in and "drop" the Free subscription from their user account. Is there any way to fix this? Is this a setting I misconfigured? Or is it just by nature something that will happen because of the way our site is set up (ie. the WooCommerce requiring user registration)?

Thanks very much!