I used to use a utility called ArtView - which added QuickLook previews for InDesign files (along with Illustrator and Photoshop) that not only showed the preview image, but a list of fonts used in the document, colors, plates, images placed, etc.
It worked great for a while. Then all of a sudden, it just stopped working completely. All the QuickLook previews were just blank.
My point is, QuickLook is buggy when additional plugins and alterations/hacks are installed or applied. QL Plugins are buggy as well. They work. Then they don't work. Then they work again. It's enough to drive you mad. Your particular problem may not be related to Quark documents at all. But QuickLooking any document invokes all the QuickLook plugins at once, so it crashes QL regardless of the document.
Sometimes you're the windshield, sometimes you're the bug.