QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still

Dear all,

After a very long google research, I would like to understand if the warning:
QSqlDatabasePrivate::removeDatabase: connection 'qt_sql_default_connection' is still in use, all queries will cease to work.
is something dangerous or not. I'm using mysql as sqlserver for a local application, and everytime I close it this warning appears.
I'm using functions like close(), removeDatabase(), deleting my QSqlDatabase pointer, but I cannot remove this warning.
Thank you very much.