Yeh i put it on the stand and then rotate but with or without pressing front break before.
But, did you ride it some distance to the stop, or just roll it to the stand? There is a big difference, as just rolling it from where you parked will not help the pads retract.
I checked a lot of videos about that and everyone is saying that there is no mechanism to retract pads from disk, they always sit on disk and have a bit of drag. One can experiment with them by gluing back of the pads to disk piston so that they retract with piston if there as that much space. I will check if they have space to backup or no.
In fact, there is such a mechanism; the sealing ring around the piston flexes when the piston extends to apply the brake, and that small amount of flex pulls the piston back a few hundredths of an inch. This small distance removes most pressure from the pad, even though it may still lightly touch the rotor. In any case, there isn't enough drag to use up much power; I suspect your lights pull more power from the engine than your brake.
Disk system is clean, nothing on it, not even dust.
I'll take your word for it, but it is VERY hard to see into the gap between the piston and cylinder, so, unless you take the wheel or caliper off and look with a bright light, you can't really know if there is stuff stuck in there. If you do remove either, make sure to stick something between the pads, so they can't extend too far out.