Originally Posted by jsloan

There was a move earlier to give free E+ on domestic flights that connect to Premium Plus; UA is booking those tickets into B. So, I suspect what you're seeing is a side-effect of that. This is different from the B fares that they set up that were using a differential price structure to track with the lowest economy fare. Nobody is paying a $700 fare difference on a domestic fare in order to get E+.

Now, you could still be correct -- this could be a precursor to DL-style "upgrades" into E+ -- but the simplest explanation is that it's just the way that they found to give E+ to PE customers.