It seems there is something defective on this lamp.
Could be wrong material fro the "rubber" sleeve (I doubt there could be anything else than a silicone, due to the heat exposure). Or its processing was faulty, so the components haven't reacted properly how they should.
To be honest, what is strange for me is using ANY rubber, even silicone, on a thing like an incandescent. Are you sure it is really intended to stay on the bulb for its service (and isn't there just to provide handling protection but it should be removed on installation)?
Yeah its supposed to stay on, the box says nothing about removing it and Its there that if you drop the bulb it dosnt' explode into thousands of pieces of glass it just sorta malformes like car front windshield glass.