sometimes (no guess, when and why) SC automatically changes the screenshot directory to C:\ after deleting an image. I saw this the second time now. Just pressed <shift+del>. SC removed the file and opened C:\ as new directory.
An additional bug in the details view: Press <ctrl+d>, if thumbnail view is active. Klick on ".." to go one step up in the directory tree. Klick on "Screenshots" to go back to the original screenshot directory. You will find it EMPTY. Pressing <ctrl+d> againg solves the problem and SC displays the content of the directory.