MySQL Workbench Tabs refuse to close
That's actually a bug. MySQL Workbench saves the tabs on close of the connection. To get rid of the unwanted tabs you could temporarily switch off the snapshot feature:
If you like to get that bug fixed file a bug report at http://bugs.mysql.com.
It's already solved in MySQL Workbench 6.3, I've just tested it an it works (it keeps only the previous tabs between sessions).