Steps to reproduce:

Create new SynchronousSample.
Run validation on SynchronousSample bpel process. It should be successful.
Open the SynchronousSample.wsdl file
make this file malformed - i.e. remove the last character in the file.
change:
</definitions>
to 
</definitions

This will make the wsdl file malformed. If you run the WSDL validation explictly
from the WSDL editor you will be told - correctly:

C:/Documents and
Settings/Mike/SynchronousSample41/SynchronousSample41/src/SynchronousSample.wsdl:44,1
XML document structures must start and end within the same entity.

Now, go back to the SynchronousSample.bpel editor.
Run the Validate XML action in the BPEL Design view (or source view )

The BPEL validator will report that there are 10 errors in the BPEL file.
However, it does not report ANY problem with the WSDL file. 
This is incorrect.  It should report the same thing that the explicit validation
action on WSDL editor reported.

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I believe this is just an oversight in our BPEL validation logic. We do have
special logic in BPEL validation that determines if the BPEL file is malformed.
If it is malformed, then the BPEL validation will pass the XML validation
sub-system the BPEL file instead of the BPEL object model That logic assures
that a malformed BPEL file is properly validated by XML validation routine.

Basically, the BPEL validation subsystem needs to add similar conditional logic
to handle cases where the upstream artifacts - WSDL and Schema are malformed. In
such cases we need to pass file not OM to xml validation. 

I assume this is responsibility of BPEL validation system. If it is not BPEL
responsibility then we must re-assign this bug to WSDL or XSD team.