Get a desk with a glass top, WD40 on the bottom of the leg, or wipe your desk to make sure that there isn't anything causing friction? Alternatively you could jam something like folded paper in where the clips rest to keep it propped out. Having the legs popped out is more comfortable, and doesn't cause any strain typing for hours every day over a period of decades, that's my experience anyways. You can also hide stuff under the keyboard better when the legs are popped up.
