This problem only occurs when TotalFinder is running.
Ever since I upgraded to El Capitan (and maybe Yosemite too), when I hit the space bar to QuickLook preview a file (like a pdf or picture), I typically see the file preview for a second in the QuickLook window, then the preview switches to the containing folder instead (I just see the upscaled folder icon with its name above). If I keep the preview window open and use the arrow keys to go down and preview other files, it will either first display the file for a split second before switching to the folder icon once again, or skip the actual file preview altogether and display the folder icon right from the start. Either way it ends up being a very erratic experience in which I can’t consistently QuickLook preview my files.
Anybody had this before and/or has an idea how to solve it?