I have suggested that several times. It might also be feeding a voltage doubler circuit, since the current required is only a little.Conductors for a winding that are connected in parallel with each other are not going to increase the voltage output.
Have you done the turns/volt test?
It would appear that the 400v (~170v) winding could be connected in the auto transformer mode i.e. in series with the 240v supply. and the total equal to 400v?
AND, here is an interesting thought. Since that winding was done with a much different kind of wire, possibly the transformer has been repaired once before.
I asked the TS to examine the circuit on the PCB to see if it might be a voltage doubler, I have not got a response back on that yet.
A voltage double provide twice the peak to peak voltage at no load current and light loads, so it would work very well for an insulation breakdown test supply.