Vue units without form, and add units or forms

[Jean-Marc]

I was expecting that units not having form should be considered as part of the project when adding them, but it seems that they are never shown while selecting View>Units, and they must be opened from File>Open.  Is that the normal behaviour ?
Also, after adding an existing form to a project, this form does not appear in Project>Options>Forms, and is making debugger error.  How can I add such a form without creating a new one and remake all the work already done ?
Platform: Linux