XML Validator in Custom Pipeline

I'm using a custom pipeline to perform message validation against the schema. I'm using XML Disassembler, XML Validator and Party Resolution in the pipeline as components.

 However the validator is not generating errors on certain conditions as mentioned below.

1. If a DateTime Tag is missing from the incoming message, no error is generated.

2. If a required attribute is missing from the incoming message, no error is generated.

The above situation is not occuring at all times, sometimes it does generate errors. However it seems it is not validating all the fields of a schema against the incoming message.

Can anyone advice regarding it at the earliest.

Thanks.