I had this problem in Panel Editor. Thankfully as I was working my way through I was saving A NEW FILE every 10-15 minutes because there is no undo option.
I was working away and went to open a menu and it went garbled and superimposed as well. I did all the same things you did to remedy but nothing worked in that file.
Thankfully I was able to go back to the previous one and it worked just fine and has continued working. If you didn't save regularly, you may be able to get a previous version of layout file by right-clicking on the folder it lives in, pick "previous versions" or "restore previous version". It will open a dialog and allow you to choose a version prior to when the problem came about. SOME pc's don't have previous version enabled so you mileage may very.?
Wayne Swearingen