Thats great news!
I was wrestling with this problem long time, finally it is usable againt!
I will soon post solution how to fix broken calendar!
Why this occurs is described:
Zimbra 4.5.7+High CPU usage with Thunderbird+Lightning.
I'm really disappointed that zimbra team hasn't found any user friendly solution for this problem
It doesn't only occur with thunderbird but with mac also!!
I really hope post one almost user friendly solution.
Back to this topic, if anyone got tasks working with lightning share your experience!