There is a bug in dell display manager (DDM). The Easy Arrange functionality doesn't seem to work if you are using font & element scaling in Windows. The windows snap to wrong positions. In my windows 7 I have set font & element scaling in display > make text and other items larger or smaller. If I use 100%, it works. I think this applies to all windows versions. I hope you can fix this.
win7, ddm 1.586