[Inf-IT DAVcl] Changing events "kills" the categorie field of TB

Hello, when an event is changed in CalDAVZap, it "kills" the categorie assigned with Thunderbird. Don't know,if TB use ainofficialextension DAViCal supports. Categories assigned in TB are f.e not shown in iOS. ButiOS doesn't touch this field if an event is changed (with iOS). Best regards, Rudolf