I've created a new dialog using the 'New Dialog...' wizard. I used the Skinnable Dialog template so it will use the same skin as the rest of the project. I've added three bitmap components, each containing a BMP file. When the dialog displays, the areas of the bitmaps that are grey are shown transparently. The bitmap component does not have a transparent flag, so I don't know why this is happening.
If I look at the properties of this element in a resource editor, the transparent property is False.
To make sure the problem wasn't related to my project, I created a new test project and imported the ISD file for the dialog I created. The same problem occurs.
