Steps to reproduce:

1. Create new eZ Publish 4.7 installation, set with 3 languages. Used eng-GB, nor-NO and por-PT;
2. Install all available service packs;
3. Create the following structure:

Home
--Folder 1 (eng-GB)
----Article 1 (eng-GB, nor-NO)
--Folder 2 (nor-NO)
----Article 1 (eng-GB, nor-NO)

4. Go to Folder 2's "Translations" tab, uncheck "Use the main language if there is no prioritized translation." option, and click on the "Update" button;
5. Go to Article 1's "locations" tab, and selected "Home / Folder 2 / Article 1" as the main location;
6. Edit admin siteaccess site.ini [RegionalSettings], and set "ShowUntranslatedObjects=disabled" and also comment out "SiteLanguageList[]=nor-NO":

[RegionalSettings]
Locale=eng-GB
ContentObjectLocale=eng-GB
ShowUntranslatedObjects=disabled
SiteLanguageList[]=eng-GB
# SiteLanguageList[]=nor-NO
SiteLanguageList[]=por-PT
TextTranslation=disabled

7. Go to Folder 1, edit Article 1 in new translation, choose language 3 (por-PT in my tests) and publish. The following error is generated:

The draft could not be stored.

The following locations are invalid:
* A node in the node assignment list has been deleted.
* No main node selected, please select one.