Hi Rosco,
What kind of material have you been plunge cutting into...?
I also use my TS saws for doing a fair bit of plunge cutting (kitchen sink and hob cutouts mainly) and have found the blades do tend to deflect slightly more when doing so than when you plunge the saw at the start of a board or panel, then make the cut. Obviously, you have more of the teeth in contact with the material at one time than the other.
I can't see how having the blade sharpened would affect its cutting width, unless the blade has somehow got inadvertently bent slightly and is now cutting wider than its 2.2mm kerf.....!