Why is a disconnected bone still following its former parent? I've disconnected 2 bones, with Alt P > Disconnect. They are definitely disconnected - they move independently in Edit Mode and under the Properties > Bone tab > Relations no parent is shown for them. But then when I move their former parents in Pose Mode, they follow along as though there was a Keep Offset parenting on them. That shouldn't happen, right? I've tried it several times. There's no constraint on the disconnected bone, no drivers.
you have to really delete the parenting. In edit mode select your bone, in bone's options tab it's parent should appear, click X.



But the real problem was...

In pose mode, adding a constraint that needs a target (IK, track,...) with hotkey Ctrl+Shift+C should be done selecting it (the target) first, then the bone to constraint. If you don't select a target, an empty is added and becomes the target. This won't happen using the constraint menu.