I have the same problem with the object BUS2200. I tried to cutomize my own Z smartform for de e-mail body. I implement the badi BBP_OUTPUT_COVER_SF. I put a break inside the badi, the variables change to the new values but the form never is called always call the standard form (BBP_OUTPUT_COVER).
I am using "External comunication" with adobe forms.
IF iv_object_type = 'BUS2200'.
IF cv_smartform_mail IS INITIAL.
cv_smartform_mail = 'ZBP_OUTPUT_COVER_TEMA'.
ENDIF.
ENDIF.