Incorrect power source after detaching a powered item

In example, a wheel is powered from a large battery and has a small battery attached (with command disk) via a side detacher.
If the wheel is operational, power is drawn from the large battery only as expected but if the small battery plus command disk are separated (ejected) whilst the wheel is operational, then power is then drawn from the detached small battery only (large battery with wheel no longer drains).
If the wheel is manually switched off, the drain to the small detached battery stops.
It is expected that once detached, the small battery should no longer be able to supply power to the wheel and that the wheel would get its power from the battery to which it is attached.
This bug was noticed whilst using a staged rover where I could not understand where my power was going after a separation.