Form validation not launched when interface called from record view

It is a FormLayout with submit button, that works as a standalone: validation before the startprocess is fired.

However, if I make it an interface called from a record view, it stops working: the process starts without the validation being done (basic "required" info).

Here is the simplified code for the form:

    a!formLayout(
      contents: {
          a!columnsLayout(
            columns: {
              a!columnLayout(
                contents: {
                  a!textField(
                    label: "Numéro article",
                    labelPosition: "ADJACENT",
                    value: ri!record['recordType!{b3cc31cc-1595-401f-b13c-16b953dd1f5b}ED Projet.fields.{b0296e3d-29b7-42e8-acd8-a99e9fd26649}budgetPrevisionnel'],
                    saveInto: ri!record['recordType!{b3cc31cc-1595-401f-b13c-16b953dd1f5b}ED Projet.fields.{b0296e3d-29b7-42e8-acd8-a99e9fd26649}budgetPrevisionnel'],
                    required: true
                  ),
                },
              ),
            },
          ),
      },
      buttons: a!buttonLayout(
        primaryButtons: {
          a!buttonWidget(
            label: "do",
            saveInto: {
              a!startProcess(
                processModel: cons!ED_PM_PROJET_CREATE,
                processParameters: {
                  cancel: false, 
                  projet: ri!record, 
                },
              )
            },
            submit: true,
            validate: true
          )
        },
      )
    )

The interface has good behaviour (validation fires) as a standalone when I test it,

but when I call it from the record view, it doesn't work anymore.

How could I make it work as I thought it would? I really need this button to start manually the process, because I want to redirect to another record, and I don't know if Appian will  let me do this with normal actions.

Thanks!