We started to migrate our project from Struts 220.127.116.11 to 2.3.1 (also tested with 18.104.22.168)
We currently use the server validation using XML validators with ActionClass-alias-validator.xml syntax.
Our interceptor stack is correctly configured having :
<interceptor-ref name="validation" />
<interceptor-ref name="workflow" />
Since this migration, our tests are resulting in database constraints violation because it seems that the validation is not called anymore.
Problem is solved when coming back to version 22.214.171.124
I have checked online documentation (http://struts.apache.org/126.96.36.199/docs/validation.html) but I can't see any change done from 188.8.131.52
The only similar issue I have found is https://issues.apache.org/jira/browse/WW-3736 but is on Client side, could be a potential clue.