How to reproduce the issue

• Start the application with gradle appRun or .\gradlew.bat appRun;
• Open the application in the browser;
• Open a modal window by clicking on the "Open the window!" link;
• Open one of Select2 Select or MultiSelect;
• Click anywhere inside of the Modal Window: the select drop does not collapse because onmousedown="Wicket.Event.stop(event);" in the modal.js swallows it;
• Click anywhere outside of the Modal Window: select drop collapses as expected.

Related issues:

• https://issues.apache.org/jira/browse/WICKET-5552
• wicketstuff/core#470