תמורה לד.
"כל הנקברין לא ישרפו וכל הנשרפין לא יקברו"
All איסורי הנאה (one may not have benefit from) that must be buried, may not be burned and that which must be burned, may not be buried. Rashi explains that one may not bury something that requires burning because we are חושש someone might dig it up and benefit from it.
The Minchas Chinuch (קמו:יז)asks: why does Rashi give this concern as the reason? Why not just answer simply that if the Torah requires one to burn something until it becomes ashes, then by burying it and not burning it, he is not fulfilling the חיוב דאורייתא? R’ Akiva Eiger zt”l in גליון הש"ס asks the same question. Both the Minchas Chinuch and R’ Akiva Eiger "בלייב" with a צ"ע.
In the חידושי הגרי"ז the Brisker Rav answers that Rashi is referring to a case where one is an אונס and is unable to start a fire to burn it. Nevertheless, he still shouldn’t bury it because it might get dug up and lead to a תקלה.