Dimensional UoM resets to 'm' after saving new product

[Lvthoog]

Module

product_dimensional_uom

Describe the bug

When creating a new product and manually selecting a Dimensional UoM (e.g. "cm"), the value is automatically reset to "m" after saving the product.

To Reproduce

Affected versions: 16.0, 17.0, 18.0

Steps to reproduce the behavior:

1. Go to Products and click "Create"
2. Enter a product name
3. In the "Dimensional UoM" field, select a unit other than "m", for example "cm"
4. Click "Save"
5. Observe that the field value has changed back to "m"

Expected behavior
The manually selected Dimensional UoM (e.g. "cm") should be preserved after saving the product.

Additional context
Tested using OCA/product-attribute on versions 16.0, 17.0, and 18.0.
No error is shown, but the saved data does not match the user input.
Behavior occurs both in clean installs and runboat test environments.
Issue occurs regardless of the selected product unit of measure (UoM).