In the first flight of v1.1, the first stage tested re-ignition in demonstration of reentry velocity reduction for stage recovery in future. The second stage also tested engine restart but failed in this flight. At this time they were still focus on getting recovery of first stage work. Elon Musk gave up the recovery of the F9 second stage as early as late 2014. He then refloat the idea later after first stage achieved recovery, but eventually he gave it up in a 2018 tweet.
In the 15 flight of v1.1, the second stage were mostly used to push the payload into higher orbit such as GTO. In these orbit insertion burn, controlled reentry were not performed. Actually controlled reentry had been performed only on three flights F9-10, F9-12, F9-19. In a highly elliptical orbit such as 295 x 80000 x 20.8 GTO, the second stage would face drag when flying pass low orbit, and would typically enter uncontrolled reentry in about 6 months. So in the first 20 F9 flights, only 3 were controlled reentry, they performed it when possible, and omitted it when it couldn't be done.
As for the difficulties and considerations SpaceX went through for second stage recovery:
So in order to accomplish a second stage propulsive landing, SpaceX would have to equip the second stage with at least a heat shield, additional SuperDraco engines, landing legs, and some kind of a system to protect the fragile vacuum engine (alternatively, there could be a mechanism that would jettison the nozzle before reentry). Elon Musk said on Twitter that it was definitely possible to get the second stage back and was "just a question of how much weight we need to add" (meaning the extra weight of a heat shield, additional engines and other hardware).
Related link: Canceled SpaceX Projects: Falcon Rocket with a Reusable Upper Stage
