I noticed when selecting a negative UTC offset such as UTC-4 or a location with a negative offset causes the offset to double. It's currently 7:10am UTC-4 however my server is claiming it's 3:10am. If I set it to UTC+1 it reads the correct value of 12:10pm.
The time on the server is correct, Piwik reads it as 11:10am UTC, however the timezone is set to EDT in Ubuntu. Not sure if that helps.
I'm using 1.2.1.
Where are you seeing the offsets doubling?
Can you grab a copy of Piwik from svn and run the unit tests on your machine?
In the "Visitors in Real Time" widget.
Checked out the latest (4151), still reads 1.2.1 on the Dashboard (not sure if it's supposed to change.)
The issue is still there, currently claiming it's 04:55 when it's 08.55.