Calendar ignores start date

Steps to reproduce

1. Schedule campaigns in the same month with staggered start dates (See attached for example).
2.  Open Calendar

Expected results

1. It is reasonable to expect the calendar to acknowledge the specified start dates.

Actual results

1. Seemingly all events active in a given month are displayed. The configured start date is ignored.

Development notes

See attached screenshots for examples from a supermarket demonstration. The campaign Comic Relief + Mothers' Day is due to start on 6th March and the campaign Easter + Comic Relief is due to start on 15th March. However, as shown in the calendar screenshot, both are displayed as valid for 2nd March.