A bug appears when you log into the demodb database, then run from a command line:
cubrid server stop demodb
for example. I attached a sample screenshot of the error. It happens for any database you connect to do, then stop from console.
Basically, it should report that the database server is no longer running and close the CM connection smoothly.
Currently, it displays "stat of database (demodb) not found" and after you press ok, nothing changes. If you try to view tables for example, then it gives the standard "Cannot get a connection ..." (see error.png).
Also, the error message in error.png is partially confusing in the second part. It should be something like:
"Cannot get a connection. Please make sure that the database server and broker are running and check that the broker port and JDBC version are correct."