Just to be clear, operating the front brake will have no effect on the rear until the Secondary Master Cylinder sees rotation force from the front wheel acting on the SMC. So being on the center stand and spinning the rear wheel the front brake has no effect on the rear. (If my memory serves me well?)
The center piston of the left front caliper is operated by the rear brake pedal, and it's bled via the left front caliper center bleed valve, try this and a bleed of the rear caliper via the rear caliper outer bleed valve. Hopefully that will clear any air you may have in the rear system.