My oil pressure is normal at startup, run up and while flying. I noticed that after flying when I pull up to the ramp and lower the rpm's, oil pressure begins to drop as it should then at about 2100 rpm the oil pressure begins to rise. As I lower the rpm to 1800, oil pressure will rise to about 50psi before slowly settling back down to mid 40's. I have cross checked with a manual oil gauge so I have eliminated that as a fault. I also have the mushroom style oil pressure relief gadget. Oil pressure is always in the green but having it rise at idle is a mystery. Also, since it only does this after taxiing back to the ramp, it may have been going on for a while and just didn't notice. Any ideas or thoughts would be appreciated.