There is a resource integration process that is running in Clarity that changes a resource's base calendar . When that change is made, details from the previous calendar are not present in the new one.
XOG is working as designed. When you xog in a change to a resource's base calendar, the data from the previous calendar is not retained.
One possible solution when changing a base calendar for a resource, is to use xog to read out the calender data (vacation days, ...) and then xog it back in at the same time as the calendar change is made..