As some background, it is useful to understand how these seals are made. The top, bottom, and sides are all extrusions which are constant cross section and come out of a die like the play dough pumper into baths to cool. They are then cut to length. The ends of the cut pieces are stuck into molds of the corners and rubber is injected to bond to the extrusions and form the corners.
The extruded sections are very stretchy where the corners are hard. When putting them on the glass, you should start in the middle and work to the corners so that the stretching that takes place pushes the corners out.
I need to see a picture, but it sounds like the corner is under tension and is twisting.
To eliminate the question of quality, I would remove the glass and remove the seal from the glass then try and seat just the corner piece on the body leaving it sit for a while. If it fits like a glove and stays like that it is good. If not, you have a bad corner molding. The other possibility is short extrusions. I would put the seal to the body working from the middle and stretching the extrusion to the corners then seat the corners and leave it alone for a while. If it keeps looking good, you have a good seal. If not you have short extrusions.
