I saw this issue a while ago.
When the option to store the chatroom messages is enabled, everything you type in the staff pool, would be visible on the main pool, for everyone after signing out and back in. That is a privacy issues for the staff of a certain chatroom if they use to keep staff meeting in chat staff pool or talk sensitive information.
2. Go back on main and all messages sent in staff pool would appear for everyone (from guests to main owners).