This feature is interesting if an Issue is a duplicate of another Issue.
Log in to the HTML5 client.
Select the Issues Center workspace, Issues Grid.
Click on the Open button available on the right-hand side of the Issue Name to open the Issue Card.
In the Issue Card, click on the Connections button to activate the Connections section.
In the Connections section, click on the Connect to Existing Issue button.
In the Global Issues list, select an Issue.
Issues are now connected to each other.