Yes, the deletion of the membershipreviewlist occurs during deployment to ensure a successful upgrade of the FBA Pack. I figure this shouldn't be an issue as upgrading (or redeploying) of the FBA Pack should be a pretty rare occurence. Also, approved memberships
are automatically removed from the membership review list, so the review list should only contain pending and rejected entries. I have just made a note in the install / upgrade documentation for users to approve any pending memberships before an upgrade.
If you'd like to remove the deletion of the list from the code, check the feature activation event receivers - that's where the deletion is done.