There is an interesting, but sometimes confusing, issue when you create a virtual copy while you are working in the Develop module. Here's the scenario: You are working on an image and before you travel down an alternate creative path you decide to make a virtual copy before proceeding. So you use the menu command or the keyboard shortcut and... poof ...a different image is sitting there instead of your virtual copy! You go back to the Library module or look in the filmstrip and notice your virtual copy did get created. You've done this before and it worked. So what's going on?
When you create a virtual copy in the Develop module Lightroom (1) creates the virtual copy, (2) deselects the original, and (3) selects the virtual copy. So you are left with your virtual copy waiting to be processed. That works so long as your original image is the ONLY one selected when you start the process.
If you select multiple images either in the Library module before you enter the Develop module, or you select multiple images in the filmstrip then Lightroom gets caught by a conflict. When you create that virtual copy and Lightroom deselects the original image it immediately selects another image in your selection set. So it never gets to step 3 and your virtual copy doesn't get selected as usual.
So if you like to create virtual copies while in the Develop module remember to only select one image at a time. Remember that Lightroom keeps the filmstrip at the bottom of each module so you can access your images easily without going back to the Library module.