while I had no problems with Spark 1.1.4 it seems that this problem is back. Not sure if you changed some d3d parameters for Spark 2.0.7, I did not change my computer, java version (1.5.0_06) or gfx drivers.
While minimizing to TNA and maximizing did not help this grey box disappeared after some minutes, without restarting Spark while I was writing this post.