Quick edit clears out custom taxonomy values

I’ve set up a custom field type called ‘businesses’ with a custom taxonomy called ‘business types’. Everything works fine until I use Quick Edit. If I change the title or date of the post using Quick Edit, any previously set custom taxonomy is removed. I’m not using a plugin for either the custom post types or taxonomies — just my own code in functions.php (which I can make available if it’s helpful). This sort of seems like a bug. Has anyone come across something like this?

Thanks in advance for any help.

Tom