I am not sure, but I think they may be ultrasonic welded together in the first place so no glue is used.
But because the two parts are made of slightly different material they expand and contract differently as they get hot/cold and this causes the wleded seam to delaminate over time.
This did happen to lots of brands between 04 & 06
But my old 08 REV1's last me three years without one valve come unstuck, so they must have sorted it out