It's mostly a northeast issue and they're attempting to make equipment upgrades as time and $$ permits, but the entire grid is designed this way, so it will take a considerable amount of time to correct.
The problem is not necessarily confined to substations, for example, lets say the utility equipment at the street is 12kV and the utility protection relays there fail when the warehouse complex it feeds is shut down on the weekend and the 1MW roof mounted PV array backfeeds the grid, then on Monday there's a fault in the U/G 12kV feed to the building and the OCP device at the street fails to open because it can't sense the fault, this would mean the next in line OCP device should open, but it doesn't, and so on.....
Several of the large roof arrays we've done have required the replacement of the buildings main 2500-4000 amp breaker(s) and GFI protection because the GFI relays would burn up if backfed, the breakers themselves were rated for backfeed, but not the older GFI units. That can get VERY pricey very quickly, especially if it wasn't taken into consideration when the job was bid.
Several jurisdictions here have required a letter from the manufacturer stating that not only is the breaker listed for reverse feed, but so it the GFI protection associated with it.
There's no way to know how many installations around the country have burnt up GFI protection since you won't know until an event occurs.
For this reason we make every effort to tap the PV feed in ahead of the main unless that is economically or logistically unfeasible because of space or feeder length issues.
