If the one clears the start date of an event in the incidenceeditor, it's still possible to save the event, resulting in an event without dtstart. This is invalid according to the RFC 5545, although it is not explicitly forbidden in rfc2445 (the predecessor rfc).
Since I generally think we should comply to RFC5545, and the event is anyways not accessible from Korganizer anymore once it has no dtstart (at least I don't know how), this should be fixed IMO by validating the event before saving (in the editor).
Steps to Reproduce:
1. Create new event
2. remove dtstart
event without dtstart
Git commit 447806f1b2c1a0ee8f703c220911661df88ec1b7 by Sergio Martins.
Committed on 14/11/2012 at 11:43.
Pushed by smartins into branch 'KDE/4.9'.
Don't allow invalid end and start times.
M +12 -0 incidenceeditor-ng/incidencedatetime.cpp