Guys, if you can consistently reproduce a Corona Bitmap looking "worse" in the viewport, please send us a sample scene. I was not able to get anything meaningful.
On the other hand, whatever is happening here, it's probably handled by 3ds Max.
You may also need to check your GPU driver settings - things like anisotropic filtering, texture filtering quality, etc. I am sure those options affect texture quality in the 3ds Max viewport.