[KevinH]

Yes a definite error. There are similar bugs with other type refinements. I will fix that before the next release.

Thanks for catching and reporting that bug.

As a work-around, you can fix it by manually editing the opf or by using custom properties in place of the broken one in the metadata editor.

Update:

Fix just pushed to master. It will appear in the next release which should happen sometime over the holidays.