Custom labels silently discarded in contacts UI

Describe the bug

When creating a contact and adding a phone number with a custom label, the label is kept in the UI when saving, but disappears after a reload.

Steps to reproduce

• Create a new contact and set an arbitrary name
• For phone number
  • click on the left-most form field with the labels (Home, Work, etc.) and type a custom string into it (e.g. "Zweithandy")
  • click on the string in the select box to make the form select your custom value.
  • Add a phone nunmber
• Hit save

You should now see a new contact with a single phone number. Left to the number, as label is shown "Zeithandy". This behaves as expected so far.

Now, reload the contact UI.

The custom label is gone. Instead the same phone number is shown, but the label on the left is "Home".

Expected behavior

As mentioned, the label is supposed to be kept and displayed left to the phone number.

Actual behavior

As mentioned, the label is replaced by "Home" after a reload.

Contact version

7.1.3

Operating system

NixOS 25.05

PHP engine version

PHP 8.3

Web server

Nginx

Database

PostgreSQL

Additional info

After the bug happened (i.e. after a reload), I downloaded a VCF file of the contact. It looks like this:

BEGIN:VCARD
VERSION:3.0
PRODID:-//Sabre//Sabre VObject 4.5.6//EN
UID:6cfa4818-7efa-4350-817b-898874f25323
FN:Jürgen Testkontakt 
ADR;TYPE=HOME:;;;;;;
EMAIL;TYPE=HOME:
NEXTCLOUD1.TEL;TYPE=HOME,VOICE:+4917864254246
NEXTCLOUD1.X-ABLABEL:Zweithandy
REV;VALUE=DATE-AND-OR-TIME:20250626T104017Z
END:VCARD

Start by reproducing the issue in the contacts UI, then inspect the saved VCF output shown in the report to trace where the custom label is persisted and reloaded. Done means the entered label remains displayed after a reload and is retained in the downloaded VCF; verify the behavior with the reported contact creation steps.