When we did this, on both doors one of the horizontal pieces fell out.We then took the door inside, laid it on top of the other door with a piece of Saran Wrap between them and glued the piece that fell out back in CAREFULLY using this glue.
Working from the INSIDE of the door (so the outside should be laying on your surface), take your piece of cane and carefully slide the sheet into ONE SIDE and THE BOTTOM.
Now you need to look to see if any areas need glue – I took my hot glue gun and shot some glue downward into the gaps from the inside of the door to keep things in place.