Windows 7 x64. Probably have all .NET versions by now (including .NET 4.0). Not sure exactly which version started doing this, but now I tried both 3.5.4 and 3.5.5. Both versions destroy the transparency, filling in white where it should be transparent. Please fix this as soon as possible. I'll look through my archives and see if I can get it to save PNG files properly using an older version. Steps to reproduce: 1) Fill an image with black and delete a portion (e.g. making it transparent). 2) Save it as PNG 24-bit. The image still looks good. 3) Now close the image and reopen it. The transparent part is white.