DA18-55 lens

I've recently purchased an *ist DS and 18-55 lens.Being new to autofocus lenses I'm concerned by slight radial movement of the moving part of the lens and wonder if it is normal.If I zoom the lens to either end of the zoom range i.e. the lens extention is at max and then hold the manual focussing ring,the front part of the lens can be moved (up/down,left/right).It won't move in/out and the images don't seem to be affected.
I have spoken to Pentax technical people and they seemed a bit vague and I got the feeling they couldn't quite see what I meant.
Has anyone else noticed this and if so is there an explanation.