Can you provide a link to the K40’s description ?
Is that a light with 3 batteries in series ? If so then the flashlight did the charging right - up to 12.6 (12.7) volts. For some reason one of the batteries got unbalanced and reached full charge earlier than two others but since the pack’s voltage hadn’t reached 12.6V the flashlight proceeded with the charging.
This is the reason why series of cells must not be charged without at least a BMS, and a balancer.
EDIT: Probably this is the flashlight, but it seems to have no built-in charger.