First I'd like to thank you for all the great new features in STK

I restarted working on the forest track, which I abandoned long ago. Currently I'm trying to get the texture splatting working properly. The textures assigned to the red, green and blue channel work fine, but the texture assigned to the black channel doesn't show up. Instead it shows just a black color. What am I doing wrong here?
This screenshot shows the problem. The black space is supposed to be the texture "forest-dollarweed1.jpg". I also tried it with a different texture, but that didn't make a difference.
I'm working with SVN revision 10917, compiled with VC9 under Windows 7, 64bit.
The forest track is attached. Please beware that this is an alpha version without any visual forest decoration (only a weird looking tree). The latest SVN version is required to run it.
Cheers,
Ivar ten Cate