I did a clean build of wx 2.6.3 patch2 (which might be important), then I did a clean build of C::B (the latest svn).
Then I started C::B, set the icon size to 16x16, and I closed it.
I fired up C::B again, but before it finished loading, I immediately focused Firefox. After C::B fully loaded itself (in the background) I switched to C::B, and there was, what I saw.