There are actually quite a few of these errors in the NWP - the people they hired to convert the dictionary to electronic format apparently didn't do a very good job. We hired someone to fix the files, but for a number of reasons that didn't work out, so we're now assessing our options and hope to have a corrected database out with the finished release of version 2.
And yes, you can indeed add your own words to the dictionary using the "Add/Edit Entry" menu command. This only works with Chinese-to-English for now, though.