Have you tried adding rich:messages?
rich:messages worked fine on the page.
I havent tried it on modal panel.
Will surely try it.
However, I want to display component specific messages besides the field and not on the top of the page.
So would prefer if the rich:message thing gets fixed up.
One more update:
I tried setting the field as required="true"
The default message does get displayed now if I leave the field blank.
But my custom message is still not visible.
I tried rich:messages on Modal Panel.
Its working fine and I'm able to get messages. However, no luck with rich:message yet.
Check documentation on how rich:message and rich:messages differ.