Commentary for Avodah Zarah 127:16

Still, the Jew does in a sense care that they should be preserved—he doesn’t want them to be stolen or lost. This is another difficulty against R. Sheshet. Again, the baraita about the convert and his idolatrous brother seems to prove that just because the Jew wants the idol to be preserved does not make it prohibited.

The difficulty is finally resolved by noting that inheritance is different. The rabbis allowed the convert to divide the inheritance in this manner because otherwise they feared that he would revert to being an idolater. After all, the loss of inheritance could be a major blow to his finances. But in a regular case of partnership, such a division is prohibited. The original baraita was not a case of a convert and therefore, since the Jew wants the idolatrous object to be preserved, it is prohibited.