Why do most Ashkenazim who wash for bread for the Melave Malka say Shir Hamaalot and Migdol (instead of Magdil) during Bentching at a Melave Malka Motzei Shabbos?
1Hi anonymous. Is there some reason you think they shouldn't be saying those things that you thought to ask why they do? Please edit to clarify. For instance, no one knows why some people say Magdil vs Migdol at different times, so it's unclear to me why you would find a particular practice questionworthy.– Double AA ♦Jan 31, 2017 at 2:34
@DoubleAA I don't think that. I just want to know why these changes are made then when it is not Shabbos or Yom Tov.– anonymousJan 31, 2017 at 2:49
1What does Shabbat and Yom Tov have to do with anything? "I don't think that." Clearly you do think that. Just edit your post to clarify since not everyone has the same background as you or understands what you want clarified. Even worse some people will think they know what you want and get it wrong and have wasted everyone's time. Best to just clarify.– Double AA ♦Jan 31, 2017 at 2:51
Many siddurim say that migdol is said whenever mussaf is said during davening (Rosh Chodesh, Shabbos, or Yom Tov). This would exclude a melavah malkah (after havdalah) and include shalosh seudos (even late but before maariv). Where have you seen it said at a melavah malkah?– sabbahillelJan 31, 2017 at 10:54
Regarding Shir Hama'alos, there are those who say Al Naharos Bavel like any other weekday (Rav Chaim Kanievsky in Sefer Sh’eilas Rav page 338) or others who say Shir Hama’alos, as on Shabbos, as long as the benching was recited before Chatzos.
Regarding migdol vs. magdil, some authorities hold that one should say say "migdol yishuot malko" like on shabbat itself, instead of "magdil yishuot"[Kaf Hachaim 189:11], while others say that one should say the regular "magdil yishuot" on Melava Malka just like during the week. [Yalkut Yosef (Kitzur Shulchan Aruch 300:4]
Perhaps the reason for the more shabbos-like (shir hama'alos & migdol) representation in benching is due to the shabbos-like quality of the meal. Meaning, Rav Berel Wein has a well written piece describing "a meal of departure in honor of the Shabbos queen prepared and eaten in order to allow us to show our love and respect for this most royal of days on the Jewish calendar." Essentially, melava malka is the final extension of the shabbos meals before fully entering the rest of the week.
Your last paragraph, the only one that answers the question, would be much improved with a source explaining that that is the reason.– Double AA ♦Jan 31, 2017 at 4:01