I have the JVC GY-HD101E with the Fujinon lens that comes with the cam.

I'm new to cameras and so on and i've been wondering if there's some problem with my lens... When I adjust the focus ring my framing changes (slightly zooms in and out) is this normal ?

Yes, it's annoying but also normal. It's called 'breathing' and is common/more obvious with lower cost zoom lenses. It's pretty bad with the stock 16x lens on the HD100.

I'm more of an editor than a camera person so perhaps someone else could give a proper explanation of why breathing occurs etc, etc...

It's the same thing that happens when you take a magnifying glass and move it closer and further from your face to get something in focus. At the same time the subject gets bigger and smaller in the glass, because the focal length is changing. A zoom lens is just a very complicated magnifying glass, the focus is basically moving the "image" backwards and forwards relative to the focal plane to get whatever you want in focus and the focal length changes as a result.

A trick to get around this is to use the macro focus ring for rack focus stuff.

Thanks alot for the quick and helpfull reply.