Dave, this is pretty flaky behavior. As you describe it, the schedule is not fully re-calculating after assigning the 4dx10h calendar (and you’ve already ruled-out the possible influence of resource calendars). In MSP 2010, I have run into something similar when experimenting with copying/pasting between projects and subprojects with different calendars. Especially when multiple projects are open – with tasks copied and pasted among them – the displayed durations become unstable, changing back and forth between correct and incorrect values just in response to cursor movements. The appearance is that the schedule is not being properly re-calculated OR Project seems loses track of the actual source data for the table that is displayed. It has helped to close the schedule files that I don’t need anymore (i.e. the sources) then manually force re-calculation of the merged/combined (but unlinked) schedule – sometimes after a save/close/open cycle.