Adding base field changed sets changed to NULL on existing entities, but do no update changed on edit

Adding base fields "created" and "changed" to eck entity type result in having "null" those fields for already existing entities.

When editing an entity, changed value wil not be updated and stay set at null.

If I change in code
$entity->set('changed', time());
$entity->save();

The value is saved correctly, and subsequent edits correctly update the changed field.

This suggests there may be a check somewhere that prevents updating the changed field if its initial value is null. I haven’t yet had time to investigate this further.