I stumbled on a foible of the "Append" operator the other day.
Attributes of type text in the input example sets are converted to type polynominal in the output example set. This has the effect that subsequent document processing will ignore the attributes.
It took a few minutes for me to work out why so I hope this will save any others these minutes. It's easy to fix, simply use the operator "Convert Nominal to Text" on the output example set.
Edit: this has been fixed in the latest release.I didn't think it was dreadfully serious but thanks to the RM developer chaps anyway.