where do you see 50M tokens being burned ?
I'm ICO investor, and initial total supply on etherscan was 450.000.000. I don't have any print screen, but I suppose someone with more technical knowledge could show us on the blockexplorer.
PYN tokens have total supply written in a contract and it's 400.000.000 Usually with preminted tokens burning means making a transaction to a special address without owner like 0x0000000000000000000000000000000000000000 I don't see such thing in a blockchain for PYN token.