Custom doctype linked in a table doesn't allow duplicate entry

Hey guys,
I need your help with a curious case:

I created two custom doctypes: Doctype 1 and Doctype 2

Doctype 1 is used to hold the a data field
Doctype 2 is used to have the Doctype 1 data field as link

Doctype 2 is then used as a table inside the Event doctype with other custom fields from Doctype 2.

The problem is when I create one Event with one Doctype 2 holding the data field mentioned above, everything is fine. But when I create a second Event with the same data field … I can’t create the Event because it’s giving the error “the data field already exists”

I have already triple checked, the data field does not have the Unique value set.

What can be the reason why I can’t reuse the same data field in two different Events ?

Thank you in advance for your help!

This issue is on v13 on Ubuntu 20

Any ideas what could cause this strange behaviour ?

Basically you can’t create a duplicate record with the same name although the Unique value is disabled.