He was not trying to. Data shows at that point JL was leading him by 8s+ with only 3 laps to go.
I think he is set on taking 2nd but trying to put a more comfortable gap on DP right after he passed him and lost it.
Lap Chart: http://resources.motogp.com/files/results/xx/2011/SPA/MotoGP/RAC/LapChart.pdf?v1_b6a7279a
Analysis by Lap: http://resources.motogp.com/files/results/xx/2011/SPA/MotoGP/RAC/analysisbylap.pdf?v1_f6f6d2c5