The reason this issue occurred is that the User Story on that feature had a matching project but did not have a release set. These configurations are required for accurate calculations once features have allocations assigned to them (which is why the user saw different things with and without an allocation)
Basically, we need the project and release to match in order to do those calculations
A little more detail: The feature is owned by Team A, but they are looking at the allocation to Team B on the plan. Points estimated, complete, etc. for Team B will only rollup if the User Story is owned by Team B (which it is), but the user story does not have a release. The project and release of the story need to match for the plan to accurately roll things up.