Problem with movement between lens and body
My ZD150 F/2 is my only lens that has that shifting between the body & lens you are talking about. I've use the combo (E5 + 150) close to two years now w/o any issues whatsoever. As others have stated, I really don't think it is anything to worry about.
If you do however look into getting the shifting resolved, be sure to let us know how much trouble it was to do so. I've learned to live with the "issue" but wouldn't mind having that solid feel you talked about between the body & lens.