Yup, went down that route today.
1 reason for the backup was the fact that it was relatively backed up to begin with and a cop with it's cherries on came by (no shoulder) causing the 3 lanes to merge to 2. Took time for flow to catch back up. Possibly an accident somewhere farther down?
Something I don't understand is how the Spadina exit gets backed up onto the live straight lanes now that the third lane is open. Prior to the lanes opening (2 lanes), you would be able to pretty much pull up to the light with maybe 5-10 cars at most.