IME...anytime a temporary profile is used...that's an indication that the standard profile is damaged.
In such cases, I would create a new profile and move the settings/files from the damaged profile...to the newly created one and then delete the old one.
As to why a profile becomes damaged...any file can become damaged at any time, IMO.
Re Quicktime...I suggest uninstalling it (it's one of my least favorite programs). If you must install/use it...then I suggest that you pay attention to all the options that you enable by default when installing it. Due to lack of info provided, I can't suggest more than that.
You may want to become a member of the QT forum, http://discussions.apple.com/category.jspa?categoryID=122