Joints don't exist in the Hierarchy. They are controls to help setup and orient bones. When a joint is translated, the length and rotation of nearby bones are being changed. For this reason, we recommend translating joints only in Setup mode and not in Animate mode (unless you are intentionally trying to change the length of your bones). Also, note that translating bones (using the Translate tool) has a similar effect: it changes the length and rotation of nearby bones. This is because bones don't actually have X and Y coordinates, but are defined by their length and rotation relative to their parent.