Hi, Reb,
This new bifurcation comes after the restaurant and the abandoned parador building where you have such a great view. It also comes after you get on the path that starts when you leave the highway at the runaway truck sign or steep descent sign or whatever that sign with all the flashing lights is.
Basically, the sign they've put in takes you off the route to San Miguel even earlier than the second turn-off (the mojon split). So, you can get to Pajares either by turning right at the new sign, or by continuing on till the second sign (the mojon), but if you stay on until the second sign you will have added 3 or 4 kms to your walk to Pajares.
I have seen one of those maps with the red dots (google? wiki?) that shows the meandering so that it would be easy for you to see where the split occurs. But of course I can't find it now. If I do, I'll let you know. Laurie