Solidworks PDM 2023
(UPDATED1: EDITED AT THE BOTTOM)

DATACARD SETUP
・set a default for a text field in the datacard to a non empty string (e.g. XXXX)

・enable "default overwrites" for the above text field

・"Updates all configuration" ENABLED on the text field

TEST SCENARIO
1. File is copied within the PDM vault (tree copy or copy & paste) 

   DEFAULT VALUE IS GENERATED AND IT REPLACES THE FIELD VALUE AS EXPECTED (XXXX is written in the field)

2.Existing file is kept checked in and a new configuration is added
   NO DEFAULT VALUE IS GENERATED AS EXPECTED (the field is copied from an existing configuration)

3.Existing file is checked out and a new configuration is added
   A DEFAULT VALUE IS GENERATED AND IT OVERWRITES THE CUSTOM PROPERTIES COPIED FROM THE EXISTING CONFIGURATIONS. THIS IS NOT A CASE DOCUMENTED IN THE USER MANUAL AND IT IS NOT EXPECTED. 
 IT IS INCONSISTENT WITH THE BEHAVIOR IN SCENARIO 2 GIVEN THE DIFFERENT OUTCOME (XXXX is written in the field or another value is carried from an existing configuration)

According to the SW user manual (highlight mine) the new configuration creation is not mentioned for default values. only a new FILE creation is. There is a mention of "new sheets" which are indeed configuration-like entities, but it seems like an exception for that case not a general rule. Note that a checked in case is not mentioned at all.
 

For many card controls, you can assign a default value to automatically fill in the control variable when a user saves a new file or item or adds it to the vault.

When a user adds a file, item, or folder from a location outside the vault, default values are written to the data card variables. If a variable is mapped to a property such as the Author property, the default value is also written to that property.

If the added or copied file or item has an existing value (for example, if the Date property is already filled), that value is used instead and no default value is written to the variable.

When a file is saved to the vault view from an application, and the application keeps the file open, default values are written only to the data card variable (that is, the database); these values might not appear in the mapped file properties until the user re-opens the file or checks it in.

When you add new sheets to a checked-out SOLIDWORKS drawing file, SOLIDWORKS PDM generates default values for the newly added sheets. SOLIDWORKS PDM updates the values in the drawing data card for all controls on the Controls toolbar. For the default value generation, you must enable the SOLIDWORKS PDM add-in before adding the new sheets.

When a user copies (or moves) a file or item and the data card has default values, the existing values are copied to the target location. No new default values are written to the variables and mapped properties (see exception below).

Digging further, according to QA00000117283 that behavior above should be expected to SERIALS generation, not for a generic text field like in the scenario above. 

Default values generate in the data card when:

• You add a new file to the file vault.

• You copy a file within the vault. 
  
  If the variable or mapped custom property have an existing value, the default value only generates when the default overwrites option is enabled.

  These default values updates in all configuration tabs in the data card, including:

• The file custom properties (@) tab.
• Configuration-specific property tabs for the SOLIDWORKS® part or assembly files.
• Sheet tabs for SOLIDWORKS drawing files.
• Model and layout tabs for DWG and DXF files.

Default values generate in the datacard also when a new configuration is added AND the file is checked out, but "Default overwrites" DOES NOT updated all configuration in that case only the new configuration tab.
 

Default serial number values behave differently depending on the Updates all configurations option. 

When the option is disabled, a unique serial number generates for each configuration tab, including the @ tab.

 

According to the above it should be triggered by "Updates all configuration" DISABLED and for SERIALS, not for our case with a plain TEXT field with updates all configurations ENABLED.

It seems that the serials behavior is applied to any variable. 
Is there a SPR or a fix for this?
I refuse to accept that this inconsistency is the expected behavior and it is in contradiction with the technical documentation.