When using dfdl:outputValueCalc, a very common idiom is to create temporary locations that evaluate when unparsing, but which have no representation in the data.
This is typically done by dfdl:length="0" dfdl:lengthKind="explicit".
If you leave off the dfdl:lengthKind="explicit" however, and the surrounding format has dfdl:lengthKind of "implicit", then the dfdl:length="0" is just silently ignored.
Similarly if dfdl:lengthKind="delimited" or "pattern" again the dfdl:length property will be ignored.
This should either be an SDE, or SDW (schema definition warning)