IPM Events - Invalid Start Date

Summary:

Getting the error "Invalid Start Date. An event start date with a duration must fall in the historical date range." when setting up events.

Has anyone had this? Am I doing something wrong or is this a bug?

Content (please ensure you mask any confidential information):

Setup calendar with all years and periods, for 24 months history and 12 month future, as below:

When attempting to add an event, it says I've got an invalid start date, even though it is within the historic periods (it does this whichever period I select).

Version (include the version you are using, if applicable):