The dropdown window is only closed when a "click" event appears.
For whatever reason, this does not happen when clicking on e.g. a button in OutSystems.
As workaround for this I changed the following JS in the OnClickDropdown action:
From:
To:
If you agree to this solution, it would be great if it could be added to the component.
If you like you can try this component too: https://www.outsystems.com/forge/component-overview/11717/advanced-dropdown-search