Bootstrap buttons - className value is not overriding base value "btn btn-default"

Hello,
I'm using editor datatables with bootstrap.
I would like to define 2 buttons for my editor modals (a "cancel" button and a "submit" button, styled with 2 different classes).

In my editor initialization options i have
[...]
formOptions: {
main: {
buttons: [
{
text: 'Chiudi',
action: function () {
this.close();
}
},
{
text: 'Conferma',
className: 'btn btn-primary',
action: function () {
this.submit();
}
}
]
},
inline: {
onBlur: 'submit',
submit: 'allIfChanged'
}
}
[...]

All is working file, but in the rendered buttons I see something like this:

The "submit" (Conferma) button still have the btn-default class, and doesn't styles correctly.

Can anyone help me with this?

Thanks