Problem with addition transition

I am working on a tutorial DVD for the Blender Foundation, and I am using Kdenlive to edit it. Part of my process is to create black and white images, and then use the addition transition to overlay it on the video.

Unfortunately, this is causing a slight change in the colors, which appears as a sudden abrupt change during playback. It _does_ show up in the final output render as well, otherwise I would not care.

You can see the problem by flipping between these two screen shots:

http://storage.cessen.com/perm/2011/kdenlive/kdenlive_addition_before.png
http://storage.cessen.com/perm/2011/kdenlive/kdenlive_addition_after.png

I am using Xubuntu 11.10, with a self-built Kdenlive 0.8.1 (git revision 77cb8f6b07814de5312aa86751ec55236529f4b5). This problem also shows up in 0.7.8, so it appears to be a long-standing issue, not just because I am using bleeding-edge builds (which I understand is at my own risk).

I am wondering if I am doing something incorrectly that is resulting in this problem (please ask me for any additional needed information). Do other people have this issue as well?