Automatic Timezone Weirdness

Question

Hi, my application is going to be accessed globally, across multiple timezones, and up until now I've not enabled automatic timezone support, and just clarified all my date labels saying "Date (GMT-6)", as my database is GMT-6.
All my date fields have always been "timestamp with local timezone", and they've all displayed as say "19-JAN-2011 04:56 -06:00" (I'm using sysdate to update the time), and it's all worked solid and consistently, so long as you don't mind working out your local time using the offset displayed. In the database for that value, it stores "19-JAN-11 04.56.00.000000 AM" - ie. the local time to the DB.
However, wanting to tidy up the app for the users, I've attempted to use automatic timezone support in my version - 4.0.2.
It's my understanding that as I'm already using timestamp with local tz fields, all I should need to do is enable automatic timezone support, and it should work out the offset automatically, and display local times to my users. If I do this, all my timestamps set before I made the change display in the correct local time (ie. the time above is now shown as 19-JAN-2011 10:56 +00:00), but any subsequent times written display as the the GMT-6 time, but with a +00:00 timezone offset shown, and in the database are now stored with a -12 hours offset.
I am in +00:00, my database is in -06:00, and so it looks like something somewhere applying the offset twice, and storing the time in the DB as -12:00, when it should be stored as -06:00 still, so it displays through the GUI correctly.
Timezones confuse me at the best of times, can anyone help??

Answer 1

This gets very strange - I've faked/changed my timezone to run some tests, and I've made subsequent timestamps a minute or two between each other, with different timezones, and can see the following dates/times stored in the DB:
19-JAN-11 05.29.02.000000 AM     -06:00 test
19-JAN-11 05.29.35.000000 AM     another -06:00 test
19-JAN-11 06.30.48.000000 AM     -07:00 test
18-JAN-11 11.32.04.000000 PM     GMT (+00:00) test
19-JAN-11 07.34.34.000000 AM     -08:00 test
Through the interface, if I'm on the same timezone as the database (-06:00), I see the times displayed as above. If I am on +00:00, I see the times above, but +6 hours. Very confusing, though I'm open to the possibility it's me being stupid... :)
EDIT: On reading that, I get the impression the calculating and displaying of the offset and time is all working, it's the storing which isn't - ie. I'd expect to see all the times in the backend database showing in the same timezone, local to the DB, which they do when I don't have automatic timezone enabled.
From the looks of it, it's applying the difference in offset to -06:00, the wrong way - ie. when UTC/GMT, 6 hours ahead of -06:00, it's subtracting that offset from the -06:00 time and storing that, making it -12:00 time in the DB. When in -07:00 timezone, (1 hour behind -06:00), it's adding that offset onto the -06:00 time and storing that.
Edited by: TimS on Jan 19, 2011 11:59 AM