Using the menu item “Collection > Rename, Add or Remove Field…” to add a new field. If you don’t provide an explicit Type the program makes an inference. In my case, it inferred “string,” which was accurate.
When the confirmation dialog appeared the final words of the text were "of type ". It’s apparent that a word is missing.
I’d suggest that (a) those words are dropped when the type is not specified, or (b) that the inferred type is used to complete the sentence.
I believe I’ve found and corrected the problem. I had a new version, 16.1.0 getting ready for release, and I’ve slipped this fix into there. Hopefully it will be out in the next day or two, and you will be able to see the results.