If the DOP is going up, the system is loosing satellite signals. DOP has nothing to do with corrections.
During the debate on the Lightsquared issue, it was pretty well admitted that our GPS receivers have front ends that are not very selective and thus subject to overloading by out of band signals. Since the frequency spectrum is very full and getting fuller by the day, this issue will continue to crop up and even get worse.
Too bad that so many claim there is no way to filter or make the GPS receivers more selective. (/sarcasm)