Only the right leg is shaking but nothing else?

Just spit-balling here... but what ever takes your focus seems to intensify. A small amount of shaking somewhere might grab your attention, then build more because you're focusing on it. I've also entertained the possibility of "blockages" in the system, as well as energy-dumps... for me, it's my eye muscles, they (apparently) serve as a convenient place to redirect energy/tension/focus when I don't know what else to do with it, or don't want to let it flow anywhere else, for what ever reason. At least that's my conjecture, but I'm none the wiser.

No weirdness or strange thing there! I get shakes, twitches, movements, parts of me jump once or pulsate hard, etc.. 

During some mindfulness and meditation practices, parts of me shake or vibrate against my will. I get these "power dumps" (or energy dumps as @clenchy said) where my prostate pulses once really hard, my head turns to the side and shakes a little, my knee will bounce up and down, my pectorals flex a few times, and my pelvis and glutes kind of flex and "thrust" once; all of these occur alone or like two different things back to back. During prostate sessions its no different. Orgasm starts to build, this "clamp down" occurs in my anus that I can't control and when it releases the autocontractions begin and I'm having an orgasm and my neck and head will move once or twice, my torso flexes, my right or left leg will shake a little or they usually slam together once or twice (I lay on my back with knees bent for sessions), stuff like that happens. I don't know why my body makes one part/limb move instead of others. It just happens.

In kundalini practice and Cobra Breath meditations, I get color flashes, some of the same movements and tense flexing for a second or two that I mentioned above, and my eyes roll around and follow the energy moving through me and I can't control any of it. When these things occur, there is a blockage or something stopping the energy from flowing freely through you. When you don't see those things anymore, or the movements don't occur anymore, the blockages are said to be free and gone, and things are moving clearly and easily through you.

It could be that we do these movements in prostate stimulation because we're tapping the root chakra center and letting energy flow through us in newer ways, and when its flowing freely, maybe the movements are lessened or not there anymore? I always get the movements due to rapid onset and strength of prostate orgasms. But in my meditation practices, the movements, colors, and vibrations are getting lesser each month.