Situation: start a query that takes some time on a particular connection.
While this query is running, try to open a table (when you would have opened the table list in the tree, this is a simple clik on the table_name in the tree) => this does not react (normal behaviour, but in previous version you got the message "Connection is currently busy. Try again?").
If you then, while this query is still running, try to open a table in another connection, this does not work neither.
The request ends up on the same stack as the other one, and will only execute after the long running query is finished or canceled, and the other table is, for a fraction of a second, opened.