Delta shaper guard incident

    About a year ago I got the Delta shaper guard, the one that consists of a rotating disk of lexan mounted on a bearing. I've used it about 3 or 4 times (since I spent most of that year remodeling the shop). Today, while starting the shaper up to run a guide template over a piece I am making, the lexan disk departed its bearing, flew like a frisbee into my shop apron (with no significant force) and landed on the floor. I know I had it mounted properly, with the, "this side down" part down, and secured to the spindle with the appropriate washers. Has anybody else had a similar experience with this device?
Upon examination, it looked like one side of the guard's center that attached to the bearing expanded and allowed the guard to fly off, there are a series of square bumps around the perimeter of the ring on one side where it came loose, the square bumps are formed by the plastic having expanded on that side.
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