As per Scalix's statement they have honoured RFC4791 http://www.rfc-editor.org/rfc/rfc4791.txt with a sort of self explaining disclaimer :
while CalDAV is based on an open Internet standard (RFC4791), implementations vary. You can find their wiki page here: http://www.scalix.com/wiki/index.php?title=TB/TB-2008-01-CALDAV
Nevertheless lightning 1.02b (http://www.mozilla.org/projects/calendar/releases/lightning1.0b2.html), at the time of this writing, still reports a quite serious list of known issues (
"By weekday" and "by day" recurrence types (such as "recur on the last weekday of the month") are not supported. -
- this sounds like a huge problem - maybe your specific event falls into this case ?). This brings me to the assumption that a beta is, overall, a beta no matter how stable to declare it to be.
Your need to stay up to date with TB is, in my very very humble opinion, arguable: TB3 vs TB2 consisted mainly in feature improvements rather than in security fixes. I personally do not love TB3 (mainly the new indexing over search folders which is almost neverending on bloated mailboxes). I decided to stay on TB2 (regularly patched) mainly due to wide availability of plug-ins like, of course, a stable non-beta working-with-scalix version of lightning, and Funambol.
This said, I'd consider the stability and security of the whole system (TB + LIGHTNING + SCALIX) instead of blaming on a single component: maybe it's Scalix's fault or maybe it's lightning (I'd point my finger on lightning as the older 0.9 is working properly).
But, again, this is my personal opinion and, plainly, it's not meant to be valid for everyone.
Bye