How to change "Edit In" behavior

I have Photoshop CC installed in the Applications folder of my startup drive, as normal.  I also have a backup drive online which backs up the startup drive each evening.  LR 5.5 insists on using PS from the backup drive for editing, instead of the copy in the Applications folder.  If I turn off the backup drive, it still refuses to start the other copy.  How can I change this?  Thanks...