Contribution Recur ID not stored against membership when renewing

Given a contact with an existing non-recurring membership, renew the membership using the front end form, selecting recurring renewal.

The value civicrm_membership.contribution_recur_id is not updated.

I have tested this in 4.4.14 & have a patch that works there but have not tested on later versions (& would ideally add a unit test to the api_v3_ContributionPage.submit suite if it is to be fixed in 4.6+)