Field value doesn't propagate even if translation is turned off

[MoritzLost]

We're seeing an issue where a Preparse field's value doesn't propagate to other sites, even if the Translation Method is set to Not translatable. This only happens if Parse before save is set to No. If this option is set to Yes, the field values propagate as expected.

Is this expected behaviour or a bug? How is the Parse before save intended to be used?

Steps to reproduce

1. Create a Preparse field in an installation with at least two sites. Set the field options as described above.
2. Add the field to a section that is active for at least two sites.
3. Save an entry in that section in one site. The Preparse field's value will only update in that site, while the other site will still have the old value.