Curiously, at some point (after I inadvertently eroded the tungsten cathode, turning the solution cloudy from tungsten residues) it became considerably more difficult to cause the same reaction, but the effect was renewed after adding another 1 ml 0.1M KOH solution.
You possibly made some Potassium Tungstate, K2O4W - easily done and it would reduce the free electrolyte. From memory it is not very soluble so would probably precipitate out.,