1: Just upgrade to Jabber 14.01 which resolved issues I had with both Jabber 12.9.5 screen locking and 14's no custom tabs showing. What I've seen a few times with 14.01 is if you click on the X in the top right corner of the Jabber screen instead of minimizing to the docked window tab, Jabber vanishes entirely. Your status changes to "offline". If you go to your start menu and click on the Jabber Icon, then jabber reappears without requiring you to sign in. It acts like the "show docked window" option is unchecked. It isn't. This oddity seems to happen the first time after upgrading to 14.01.
2: We are not using Unity for our voicemail. I've noticed that the MWI status of my desk set is not reflected in Jabber when either using Jabber to control my desk set or when using Jabber as a soft phone. With telecommuters we now have more softphone users and they are missing the MWI.
3: Our firm is moving to Office 365 with the cloud Exchange. Jabber's calendar function can't see the Outlook calendar unless a local copy of Outlook is installed on the PC. A lot of users are only using the web based client. Changing Jabber to use another calendar like Google also doesn't work as when you attempt to log into your gmail/google account Google pops up a incompatible browser error. It would be nice if Jabber could have it's own calendar option like the contacts.
I don't see the same behavior with the X changing my status - it still shows available in the tray and at the presence viewer tool.
I have the docked window off as it's irritating to me, but, clicking the X doesn't remove it from the screen.
I'm not sure, regarding MWI, how you would have had this arranged to work previously. The MWI / message count is based on API call to Unity Connection, not message counts from the line or similar.
Jabber for Windows requires Outlook to use MAPI to pull your calendar details. Jabber for Mac does not, and uses EWS, which at present is broken when Modern Auth is used, but should hopefully be fixed by the next major Jabber release. I doubt they would port this functionality over to J4W given the development on Jabber at this time, but, you could place an enhancement request through your account team to request it. It makes sense to me not to depend on MAPI, but there are probably other interrelated components (like Outlook contacts, meeting invites, presence) which will depend on it being there.