Toolbar icon background problem

I'm using the toolbar wizard in VB6 to modify a bog-standard toolbar in my application.

When I add an icon with a transparent background, the background stays transparent until the first time I run the program, and then turns black. Thereafter, it remains black until I reload the icon by using change bitmap in the toolbar wizard.

The same thing happens with icons I downloaded from the internet, icons I extracted from Windows dlls, and icons I created myself in Visual Studio.

What am I doing wrong?

Thanks

Ian