You may notice that, when you don't have any renewal window set up, expired members are still being issued renewals, which causes them to keep their old expiration date. This means that they lose some membership time.
We are currently evaluating this issue and will update this article as we learn more.
Steps to Duplicate
1. In Sales>Daily Sales, Search for a constituent who had their membership expire last month. 2. Click Memberships>Renew the membership. Save this. 3. Complete the order. 4. Go to the Constituent Record, click the membership. See that the Expiration Date is for the previous month.