Chezkas Mamon on Keifel

My son is learning hamafkid. The Mishna tells us that a watchman has the right to pay for an article stolen under his watch and thereby acquire the keifel penalty the thief would pay if caught. The gemara introducues a number of cases where it is unclear, there is a safeik, whether the watchman has purchased the rights to keifel. The RI"F paskens l'halacha that in these doubtful cases we split the keifel between the watchman and the owner. The Rosh, however, disagrees. In any monetary case of doubt there is a rule of chezkas marei kammah - whoever is the last possesor of title retains rights until proven otherwise. Since the owner of the animal retains title until we know otherwise, why would we not rule in a case of doubt that he is also entitled to keifel? A number of possible explanations could be given for the RIF. One approach is to distinguish between title on the animal or object, which exists, and title on the keifel payment, which does not exist until the thief is caught (this is not so simple a distinction to draw, as keifel is at first glance just an product of ownership, not a new thing in and of itself). The Kuntres HaSefeikos suggests that one may distinguish between a doubt between parties (safeik b'metziyus) which can be resolved by looking at who the marei kammah is, and a doubt in halacha (safek b'din) which is independent of the parties involved.