From R. Yitzchak Meir Goodman, And There Was Light, p. 284:
"...on the south side, lace hangings were of fine twisted linen...." (Shemos 38:9)
These "hangings" (kela'im) existed only in the Mishkan, but not in the Temple in Jerusalem. However, the puzzle is that in the chapter of Mishnah recited each morning [Eizehu Mekoman], we read of sacrifices to be eaten "inside of the hangings." But the Mishnah was written to guide us in Temple procedures.
The early commentators (Beis Yosef, Orach Chaim, chapter 50) state that this chapter of Mishnah was chosen for each morning's prayers as a rare, ideal one. In the entire chapter there is no disagreement between the rabbis. Why indeed is there such a rarity?
The Vilna Gaon states the reason. This chapter was rendered in its entirety, without a word changed, precisely as it was handed down to us by Moshe at Mt. Sinai! Therefore, the kela'im were of course part of the instruction at that time, and remained in the text of the mishnayos.
The Vilna Gaon, פנינם משלחן הגר"א, edited by Rav Dov Eliach