Joyce (2011) and Rinard (2013) have both discussed this problem. Rinard’s solution to it is to argue that this shows that the vacuous prior is never a legitimate state of belief. Or rather, that we only ever need to model your beliefs using non-vacuous priors, even if these are incomplete descriptions of your belief state. This is similar to Walley’s “non-exhaustive” representation of belief.  Vallinder (2018) suggests that the problem of belief inertia is quite a general one. Castro and Hart (forthcoming) use the looming danger of belief inertia to argue against what I have called an "objectivist" interpretation of IP. 