Is this an undocumented "feature"?

I just discovered that if you decide to have "Cancel" instead of "OK" as your default button, the value entered in the input field does not get recorded. In other words, if the button you choose to confirm an action with is not the default button, the input fields are left untouched.

Troughout my application, I have chosen not to take action "by default": if the users want to create a record, they have to intentionally click on the Create button (that is not the default), or if they want to print, the default is to cancel, the second button is to print.

I found that by doing so, records don't get created unecessarily and paper does not get wasted if the user trips on the enter key... (this is with a dialog)

I have experimented with global fields and regular fields, with the same outcome. This is the first time I have considered using the Input fields to create records (to do some preliminary validation before actually creating the record).

I have also tried not to have a default button at all (only use button 2 and 3) but it looks the fields input only works if the default button is used and selected.

Does someone know why the dialog function has been setup that way?

Yes, field input is only accepted when the default button is chosen. You're not the first to have trouble with this.