Maintenance plan package change resulting in incorrect call dates

When we change a maintenance package on an existing maintenance plan to a package whose frequency is not an exact multiple of the previous package (for example, changing from a 6M 180-day package to a 1Y 365-day package) and then restart the plan, the call horizon of the plan seems to be ignored and the new call dates are always a day or so before the plan date regardles

Why is the call horizon being ignored in this situation?