q on market depth

Hello

I decided not to sell today, as market depth was getting better, end of day had about 9 M buyers to 4 M sellers.

However I just checked the depth again and some 4-5 M buyers have vanished. Now, I have noticed market depth changes long after the market closes with most shares. But I do wonder who it is that can do this? When I change an order after market it doesn't show up in the 'official stats' until the next morning.

Can brokers do this? And if only brokers, why were they propping up the buy side this afternoon without any intention of buying?

PS this must be a good buy, marketcap only 11.5 M for around 400 M T copper. Any opinions?

Cheers!