Yesterday, 12:14 PM
If you select a file, then click somewhere outside of that window, the file remains selected, but is just not in focus.
If you click on that already-selected file, the system may still hold that first click, and another click registers as a second click, even though it's several seconds later. (Not saying that's correct behavior, but might explain what's happening)
If trackpad, is that the built-in one on a MacBook, or a wireless Magic trackpad?
Go into your System preferences, then Mouse, or Trackpad prefs. Make sure that "double-click speed" is NOT at either extreme.