Blunder in circuit of AC fans in T.L. coaches

Today a coach(GS 09448) arrived in Bandra in 2472 Jammutawi Express with no fans working. The battery had got drained somewhere before Ratlam, then TC was provided but that helped only lights. And the caoch came all the way from Boaroda to Bandra without a single fan working.Why?

Because of this circuit:-

Here you see that in case a TC is provided , no supply will be available to the negative of fan inverters.

BCT division has identified this problem in the begining itself and has modified many coaches of ADI division and NWR and NR by this simple modification:-

But the surprise here is how come the same error in circuit occurred in the coaches manufactured by both RCF and ICF?