When an event does not come with a DTEND the whole calendar fails to load.

With investigation evolution reports:

$ export CALDAV_DEBUG=all
$ evolution

(evolution:22592): calendar-gui-CRITICAL **: e_day_view_add_event:
assertion `start <= end' failed

To see whether this is a bug or not, I read the iCalendar spec at http://tools.ietf.org/html/rfc5545

which states:

"
For cases where a "VEVENT" calendar component specifies a "DTSTART"
property with a DATE value type but no "DTEND" nor "DURATION" property,
the event's duration is taken to be one day. For cases where a "VEVENT"
calendar component specifies a "DTSTART" property with a DATE-TIME value
type but no "DTEND" property, the event ends on the same calendar date
and time of day specified by the "DTSTART" property.
"

i.e. DTEND and DURATION are not mandatory and a DTSTART of DATE type means all day, and a DTSTART of DATE-TIME means that point in time - which needs to be calculated before it gets to the gui assert (above).