I checked this and the exe I used to publish the demo was made with the old WED. A newer wed (newer ENGINE) like for example engine Version 6.40.5 renders the motion blur absolutely perfect.
YOu can download the update on the official download page:
http://www.conitec.net/english/gstudio/download.phpThe free update directly under the trial version.
Here some screenshots I made 1 minute ago:


