In my bedroom i have drop down ceiling near the walls with recessed lighting. It has curved metal corner beads along the edges, but they are butted next to each other. Cracks are showing between the two metal corner beads that are butted together. I scrapped paint/mud off one of them and there is a 1/8 inch gap between the two. I taped it with fiberglass drywall tape and filled it with joint compound, but it just cracked in a day or so. How can I fix these cracks?