Are you sure database collation is properly set ?
The issue you describe happened to me once when I used the default setup for db charset and sometimes depending on specific configuration you have to set it manually...
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MODx est l'outil id
Quote from: Sylvaticus at Sep 17, 2008, 04:40 PM
Quote from: Sylvaticus at Sep 16, 2008, 12:59 PM
Upgraded three sites to day already. No problems at all. None.
Well, it’s no longer the absolute truth. I have big problems with special caracters according to my language, æ ø å in norwegian, special in the manager, even if I use english as the back-end language. I will find out more about it and post it on the right place. 
A custom upgrade install will let you set the character set (and see what the default is).