Hi @KMS ,
This happens because the default behavior for success type messages is to auto close, unlike the error type messages that never closes (which was the purpose of this component at the beginning). I agree that it is a bug, since the property description is confusing as it leads you to believe that the manual close will never close the box for any kind of message (sorry about that, I'll fix it).
The auto close consider the Site.TimeoutSuccess value definition to set the duration in miliseconds for the message. So, in order to keep it displayed, you could set this site property with a big value (it won't be shown forever, but maybe for time enough to attend your requirements). Of course it is a workaround. If you do really need to change the component behavior, you'll need to customize the JS inside of it.