On a membership renewal, the member's existing membership is not preselected.
After testing this with #4939 (closed), the issue still exists.
Our use case is with a membership price set, using a Select field type.
To replicate at the dmaster.demo.civicrm.org site, create a Membership Price Set, with one field. The field should be a Select type, and each of the 3 membership types should be added. Then change the existing Membership contribution page to use this price set rather than the manually entered one. Open the Live version of the contribution page, and sign up for any of the membership types and complete the transaction. Then go back to the live version of the contribution page and observe that the user's existing membership is not preselected.