Outside Corner Help

When intalling the verticore - O pieces, there is really nothing holding the top of the corner piece to the Endu-board... Has anyone noticed this? Am I installing these outside corners incorrectly? Should I use, say, some silicone or other caulk at the top to hold the corner trim piece in place? The bottom of the trim will be held in snugly with the baseboard... Also, when installing around a room, with many inside and outside corners, has someone developed a routine or standard procedure for joining panels (e.g. which panel is the verti core slot slipped on to vs. which side is just pushed up against the adjacent panel, if that makes sense?)