One forgot to recite ata chonantanu on motzoi Shabbos. Prior to reciting Havdalah on a glass of wine, one transgressed a rabbinic prohibition (whether through handling muktzah, or any other rabbinic sin). Is it necessary to repeat SE?
If a person didn’t say ata chonantanu in ma’ariv on motzei shabbos, and he also ate before saying havdalah he has to daven again. (This applies only to men, if a woman davened ma’ariv and forgot to say ata chonantanu, even if she ate she doesn’t have to daven again, since they don’t have an obligation to daven ma’ariv.) However this applied only to actually eating; if he did melacha even if it was before he even said boruch hamavdil he does not have to repeat SE.
O”CH 194-1, Shmiras Shabbos Khilchoso chap. 96 ftnt. 95 and 33, Biur Halacha 294 D”H V’im Toam, M:B ibid 3.