When the operating (moving) sliding patio door closes and locks, the other end should interlock with the stationary door (fixed panel) to seal out wind and drafts. There can be several reasons why this interlock may not perform as designed… 1. The weather seal has worn and needs to be replaced. 2. One of the doors, usually the operating door, is warped. 3. The stationary door (fixed panel) has moved away from the jamb slightly and does not allow for a good seal at the other side where the doors