Per the RichFaces documentation:
...If an invalid value is entered, it is highlighted as erroneous and validation messages appear with the submission...
The validation message is not displayed when entering an invalid value (which is not on the list) and submitting it.
Test code:
<rich:select id="idSelect" value="#{backingBean.value}" enableManualInput="true">
    <f:selectItem itemLabel="Option 1" itemValue="Option 1" />
    <f:selectItem itemLabel="Option 2" itemValue="Option 2" />  		
</rich:select>

Steps to reproduce:

checkout https://github.com/papousek/richfaces-sanbox/tree/RF-12474, build it and deploy on JBoss AS 7
open http://localhost:8080/richfaces-sandbox-jee6/
select "a" item from the first rich:select and click on the first "send" button
type "AAA" into the first rich:select and click on the first "send" button
validation message should be present, but it isn't.