This is not Corona bug. It happens to me sometimes with other renderers too. It's a bug in PNG file handler plugin of 3d Max. Only thing that really helps is resaving problematic PNG's to other format.
1 - Close 3Ds Max2 - Go to C:\Users\[YourName]\AppData\Local\Autodesk\3dsMax\2014 - 64bit3 - Delete ENU folder (I usually keep the "UI"-folder inside "en-US")4 - Restart 3Ds Max