I’ve been having the same issue as well. Pinning seems to cause the vertices around the pins to react unpredictably and ignore gravity. I made sure that there were no intersections between the cloth object and the collision object, the collision object was properly decimated, and all object transformations have also been applied. I can’t seem to figure out what the problem is. This kind of frustration with Blender’s cloth sim happens every time I’ve tried to use it for practice or otherwise. >_<;;;
I’ve included a google drive link to my .blend file and some screen shots: https://drive.google.com/open?id=0B-Nbo5YZpNanSk9ydC1CNWgwMk0
