Evolution: Set default start date for memos to "none"

In Evolution 2.28.3 on Ubuntu 10.04 64-bit, I have noticed that memos only appear in the memo pane of the weekly calendar window when the start date of the memo falls during the week shown in the calendar pane. That behavior is different from tasks, which appear regardless of the date of the task, and (to me) confusing.

Memos whose start dates are set to "none," however, appear regardless of the week shown in the calendar pane. When a new memo is started by typing in the summary column of the calendar window's memo pane, today's date is automatically assigned as the memo's start date. This means that the memo will be invisible in future weeks unless the user remembers to manually edit the start date.

Is there a way of setting the default start date for memos to "none," so that they are guaranteed always to appear?

Thanks,
Jobo