In your discussion, you didn't really say that you had tried the upgrade to the Calendar 3.2.0 (just posted on my site).  This the first actual version I have attempted supporting Upgrading from a previous versions (only Calendar version 3.0.10)...In other words, if you had previously installed AVCalendar 3.0.10, the upgrade should have kicked in automatically upgraded your data...I'm sorry about lack of upgrade planning in prior versions...but, as you've found, it's always a good idea to backup before attempting upgrades for any module or DNN core.

I'll assume you are running the new version of the Calendar and trying to reconcile how the timezone conversion works...With this module, All Events in the Database are now stored in GMT +0...and then converted to the user's time zone as needed.  The current calculation does not try to compensate for DayLightSavings time yet.  It simply performs a calculation based on the GMT Offset.  If the user is anonymous in DNN, the calculation is based on the portal/site timezone...so really, the TimeZone field in the Database is not being used...since all of the Dates are assumed to be GMT Based. 

Recommendation:

Because of this the upgrade process will need to be changed...I can 1) turn off the TimeZone Calculations as a module preference or 2) you can provide a SQL Calculation to convert all your times to GMT +0 or 3) kill the data and start over adding events (the module will perform the calculation for you.  Does this make since?

Alan

Additional information:

On a virginal 3.2.2 DNN isntallation I loaded your latest release. I created an event, then noticed the site time zone was wrong. I changed it. The event update wouldn't let me update the time zone field. It always takes the portal setting. The event displays as

As a suggestion, if we can't change the timezone it shouldn't be a dropdown that implies that we can. I understand that it's stored internally at GMT+0. My issue still remains when I'm not logged in the times should display at portal timezone, but they don't. They display properly when you click on the event and display the details, but they don't in the List on on the Calendar.