Alpha Channel with EasyWorship 7 on Atem Studio HD problem

We use Easy Worship to provide lower thirds and videos to our stream. Easy worship is able to generate an alpha channel on a second HDMI output. So I connect the Easy worship computer with to HDMI cables to the Atem Studio HD. I configure a downstream key with the fill on the first channel and the key on the alpha channel. According the documentation of Easy Worship I use the setting premultiplied key. This works fine for lower thirds and transparency blocks.

We use the alpha channel to mix subtitles and semi-transparant graphical blocks to our live stream.

TransparancySmall.jpeg (154.15 KiB) Viewed 908 times

But when I provide a solid video, with a complete white alpha channel I still see the background camera through the with parts of the video.

This is a video on top of the camera, you still see the camera through while the alpha channel is complete white.

OpaqueVideoSmall.jpeg (71.07 KiB) Viewed 908 times

So I turned off the premultiplied key and try to find settings to do this. The best I could find find results in less transparency and darker blue. Is there somebody who can tell me how to fix this? Thanks in advance.