When the location of input/output ports is changed using the Appearance editor, the old coordinates stay valid, even when moving around the subcircuit.
Example included: just move the location of the output port elsewhere. The main circuit still gets a value from the component even when the wire should no longer be connected. The subcircuit can be moved around without reconnecting, but the value stays on the wire.
Saving and reloading the file prevents the bug from happening, so I think the coordinates of the subcircuit don't get updated correctly.
This bug is present in both latest stable as latest fragile.