If I try to edit a number in a {{formatnum:…}}, the VisualEditor displays the template’s edition window, saying it is (for example) the 'formatnum:959719' template, without any parameter. So if I want to change the number, I need to remove the 'template' and then to add a new one, for example 'formatnum:958719'.
The editor should allow changing the number without having to remove the 'template'.