I had a similar problem and, not having time to investigate, found a workaround using the basic templating system:
define the butttons at the end of ad_form with commands like:
element create lineaddedit new_keep -label "Crea e mantieni" -widget submit -datatype text
element create lineaddedit new_clear -label "Crea e azzera" -widget submit -datatype text
element create lineaddedit clear -label "Azzera" -widget submit -datatype text
place the form widgets as you like referencing their id