Validation issue in Maintenance form field

[valeriocomo]

Subject of the issue

Form fields maintenance.contracts and maintenance.contractors don’t show properly a validation message, as reported in #349, issue 5.

Steps to reproduce

Add a contact or a contractors. FIll all the fields. When you add a second item, validation is fired.

Expected behaviour

Validation would be fired properly.

Actual behaviour

Validation is fired only after unrelated actions.