Field type Taxonomy doesn't save choice if other fields are empty

Hi,

I have a problem with the taxonomy field.

My code : https://ghostbin.com/paste/nwwk3

If I check one of mine categories and all fields empty (the 4 next after taxonomy selector). When I save the post, the category selected is not saved.

If I enter something on input "client" for example and I choice a category, when I save, it's ok. The category is fine.

If I erase the content on "client" and I click on save, the category is empty again.

I made a little screencast => https://youtu.be/2CE_fAJsjWs

Any ideas what's happening ? 🙁