I have a Sequence diagram using the UML markup I used a swim lane container to highlight a section of the sequence diagram for this I had arranged the sequence diagram to be in the front of the swim lane container which has a background color. This worked fine until now for some reason the swim lane has moved o the front and so it's interfering with the Sequence diagram. Even though it's arranged to be "send to back". I've tried rearranging the both the Sequence diagram and the swim lane also tried adding a new swim lane and sending it to back but it is still showing in front of the Sequence diagram.
As mentioned this happened recently and without making any changes to my diagram.