I suspect that this test is incorrect.

The test features the line:

          <p:variable name="x" select="//baz:message">
            <p:pipe step="catch" port="error"/>
            <p:namespaces element="//c:error"/>
          </p:variable>

At this point, there is no in-scope namespace binding for prefix "baz".  The 'select' attribute is compiled according to 2.6.2.1 Processor XPath Context, with "Statically known namespaces" set to "The namespace declarations in-scope for the containing element.".  This results in a statically detected compilation error for //baz:message.

The use of <p:namespaces element="//c:error"/> does not change the namespaces in-scope during compilation of the 'select' expression.  

The variable "values carry with them not only their literal or computed string value but also a set of namespaces"  These associated namespace bindings are not identical to those used to compute the value.