Yeah, I've heard of this happening in some Indian hotels. I think it happened to me at The Park, Bangalore where we had a low corporate rate but they charged taxes on the rack rate. I just informed our procurement department and I believe it has been resolved.
I have never been charged any taxes on the Intercontinental the Grand Mumbai (or the Hyatts and the Le Meridien in Mumbai either, even though I remember that while booking it said that taxes were not included in the rate on the website). Maybe its a hotel specific thing for the ICs. Delhi state taxes perhaps? Although I did read somewhere that they were going to have a nationwide VAT soon instead of the state-specific taxes.