I deal with this about once a month with my customers. I pulled a Koni rear shock and a stock rear shock mount from my inventory to demonstrate.
You MUST have a large enough washer on the top and bottom of the mount. The washer on the bottom should not be able to slide all the way down the shaft. When you do not have the proper washers installed you can punch the bushing out of the mount... especially when the washer on the bottom side of the mount is not there or not correct. Properly installed the bushing should be TIGHTLY sandwiched between 2 large washers.
It looks like you don't have a washer on the bottom. That would cause all the force from the shock to be concentrated on the small metal sleeve in the center of the bushing instead of spread out over the entire bushing surface. This concentrated force pops the bushing out of the housing.
