Are you having trouble with QGIS locking up with the Rule Based Layering Dialog? Try deleting the “UI” section of ~/.config/QGIS/QGIS2.conf. I believe but haven’t been able to confirm that the paneldialogEdit%20rule is causing the program to get confuse and not properly display the window, after the window position has been moved.

For now, once you delete that section and restart QGIS, you should avoid resizing and moving the Rule Based Layer Dialog window. I don’t know when there will be a bug fix, but this seems to fix the problem for me now.