How strange. It took me awhile to reproduce the problem because I have never seen it. But after some experimentation, I finally found that appears to be a problem in fullscreen mode only. I don't usually play in that mode, so did not notice the problem. I don't yet know what causes it, but I will figure it out. In the meantime, if you switch to windowed mode, it is fine. Sorry for the trouble and I don't know when that problem was introduced; I will look into it.