From the Material editor, when you "launch" a texture map from a texture slot by clicking on the "Launch" button, a degraded JPG image is sent to the chosen image editor instead of sending the original texture. This result in editing a degraded image with compression artifacts. Several roundtrips this way and you end up by having a seriously degraded texture map.

If you save the same texture map from the same slot by clicking the "Save" button, then you can save the image as a lossless PNG image without compression artifacts.

In short: CC2.01 (same issue with iClone btw) SHOULD send ("Launch") non degraded PNG images (or any other lossless image format) to the chosen image editor instead of lossy compressed JPG images.