[ownedbycats]

While preparing to merge two books together, I edited the first one to clear unwanted values. This included two enumerated columns, using the green recycle button.

Then when I clicked 'next' to clear unwanted values from the second book, I got this error for both columns:

calibre, version 6.16.0
ERROR: : The enumeration "Column Name" contains an invalid value that will be set to the default

I've seen this before (editing permissible values and forgetting to rename the entries afterwards). But both of the columns here had valid entries before I cleared them. What happened?

EDIT: It happened again. Specifically when I use the 'clear' button on an older enumerated value -- it doesn't replicate if I set it again. Also, the enumerated dropdown fails until I close and re-open the MDE.