Can't manually update work day unit

Double problem, installing company_work_time and updating the company work time to typical values in French service company (see attached) the uom work_time is not updated from 8 => 7.

There doesn't seem to be the link between the two!

Worse, using the tryton client to update in the configuration of the UOM worktime, the following error is raised.

Tried with trytond-console, where the following worked without any perceived errors:

>>> UOM = pool.get('product.uom')
>>> udm = UOM.search(['symbol', '=', 'jt'])
>>> udm, =udm
>>> udm.factor=7
>>> udm.on_change_factor()
Pool().get('product.uom')(10)
>>> udm.save()
>>> transaction.commit()