That's not Sinbad mixing address but the address Royse777 is paying participants from.
It is a problem if he is controlling keys for that address, but they probably added it because of connection with original sinbad address.
And that's the real problem, the fact that they posted it whiteout checking what it means, so we have two things right now
- some funds that are ( as far as I know) in Royse777 control that came from sinbad, with which he can choose to do whatever he wants, return it, send them to OLAF, screw the entire forum by sending dust to each posted address <<< seriously don't do this !!!
- an address has already go labeled as dirty, and this s*** won't get fixed, it simply won't
I've seen bad AML bots flagging exchanges addresses as bad, casino payments address as suspicious and so on, once this will spread everything that came into contact that address will become "suspicious" for these morons, so if it hasn't happened already (unsure about that screenshot someone posted) some might find themselves in trouble maybe tomorrow or in 6 months from now if they will deal with a CEX that is using one of those stupid tools.
So my advice for participants would be to try to clean whatever coins have been already received and not spent a bit before sending them to any business, and retire the address you've used to get payments till now, might sound like fearmongering to some but I'm just saying how I see things from my perspective.