I can't reproduce this no matter what I do. I assume you're talking standard tracks, right? Not Take Lanes?
If I have two clips in a track and crossfade them, I can move the "top" or "bottom" clip independently. If the clips still overlap after one of them is moved, the crossfade time adjusts to accommodate the new amount that overlaps. E.g., if one of the clips is moved further away, a smaller portion of the clips overlap, so now the crossfade is shorter.
I would like to know how to reproduce this, because there are times when moving multiple clips by only moving one would be convenient!
Are you sure they're not grouped? Does select all, right-clicking on a clip, and choosing "Remove Selected Clips from Groups" help?