Scrolling causes selected dates to change in Month view

The calendar “Month” view has a bizarre problem. If I select a date range and need to scroll down to see into the next month, the selection is changed by the scroll action. So if I select Jan 8-15 then try to scroll down to see dates below, my selection changes to Jan 15-22, as if the selection is a hovering window beneath which the dates shift.

The problem occurs whether I scroll using arrows, scrollbar, or mouse-wheel.

Altering a user’s selection conforms to no known UI standard, it’s a crippling error. If I select a date, it needs to stay-selected until I modify or de-select those dates. I mean, right? What use-case would prefer ignoring user-selection? I don’t get it.