The Shulchan Aruch changes the lashon [expression] of the Gemara in Ta’anis very slightly and it would seem that the reason he does this, is to demonstrate that we don’t go like the Machatzis HaShekel.
The Gemara, Rif, Rosh, Rambam and Tur all say: כל העושה מלאכה בת''ב אינו רואה סימן ברכה לעולם – “Anyone who does work on Tisha B’Av, won’t see any blessing forever”. Tosfos is medayek the word לעולם - forever. The Machatzis HaShekel explains Tosfos to mean, that not only will one not see any berachah from the money earned on Tisha B’Av, but throughout the year as well, if one does the particular job that he did on Tisha B’Av he still won’t see any berachah.
However, when the Shulchan Aruch brings down this Gemara he misses out the word לעולם. All the Rishonim bring down the word לעולם, so why does the Shulchan Aruch skip it out? It would seem that the Shulchan Aruch doesn’t want people to understand Tosfos the way the Machatzis HaShekel does, and for people to think that one will never see berachah from that work ever again, therefore, he misses out the word לעולם.
It could be that for this reason, the Mishnah Berurah (554:3) only cites the Elyah Rabbah who learns that one won’t see berachah from that particular money, and he doesn’t mention the Machatzis HaShekel at all.
