Midi controller gets mapped randomly to VSTs

I am currently using a NordLead as my primary midi controller, plugged into a Cubase 7.5.2 through a Profire 610 audio interface on a MAC [OSX 10.9.3] and i am facing a bit of annoying situation.

At times when I am recording audio from my NordLead and i am tweaking the knobs, out of no where, the Knobs get Mapped randomly to one of the the VSTs on some other midi track, that are in the project and it messes up that track.

For Instance, I am currently working on an ‘Audio Track’ and as i am recording audio and tweaking the [FM] Knob on the Nordlead, all of a sudden I notice that my kick is gone, and then i realize that the [FM] knob I was tweaking on the Nord has gotten automatically mapped to the Volume Control Slider in Groove agent in the Midi Track where the Kick is playing, and as i am tweaking the knob, the volume of the Kick is fluctuating. the Only solution i have for this is that once it gets mapped, i need to open up GrroveAgent and right Click, Open the Remove Control Devices Menu and then remove all Midi mapping. this seems to work for a bit and then after a while it gets remapped again, not sure why.

Another example, again i am recording audio from Nord Lead and i notice that my bass has gone, so i open my midi track where the bass is and there i am using Sylenth1 and i notice that my FM knob has now gotten mapped to “Decay Fader”, and now i need to sit and reconfig my bass. Here i dont even know how to unmap, because there is no menu on how to unmap a midi contoller.

can any one please help me out here why this is happening, and how i can prevent it.

Also if someone can tell me how i can “unmap” the Contoller to the Vsts, would be great.

thanks in advance.