If I have an existing non-fullday meeting, the ical contains values like this:
{{{
DTSTART:20131114T000000Z
DTEND:20131115T000000Z
}}}

If I edit the meeting and enable the fullday toggle, nothing changes in the ical (it should change to VALUE=DATE: format). Also when I edit the meeting again, the fullday toggle is off (should be on).

Similarly, if I create a new fullday meeting, the ical contains something like this:
{{{
DTSTART;VALUE=DATE:20131123
DTEND;VALUE=DATE:20131124
}}}
When I edit the meeting, disable the fullday toggle and change the duration to just a single hour, the ical output does not change (should change to traditional hour format). When I edit the meeting, the toggle is again on (should be off). Quite interestingly, the fedocal web calendar shows the meeting correctly (1 hour duration). But none of the third-party clients would, because ical is wrong.

The only workaround seems to be to remove the existing meeting and create a new one.