You should not have changed your timezone though, but simply turned of daylight saving. (And If you have Windows XP, this will be done automatically). Thus, your timezone should be
GMT-3 hours, with
DST off or if you have Windows XP, as shown in the screenshot (click on it to see it full screen):
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As for the deletion of the logs: I tried to reproduce it, but nothing is deleted here though...
What is your full Messenger Plus! version? (it would be in the form of 3.
XX.
XXX and can be found by going to
the main Plus! menu > About...)