Hm, given that your for loop isn't inside of any function, it means that your file is read more than once.
Are you sure that it isn't referred in an xml file or somewhere else more than once?
Code:
<Ui xmlns="http://www.blizzard.com/wow/ui/">
<Script file="file.lua"/>
<Script file="file.lua"/>
</Ui>
The content of file.lua will be read twice in this case, and everything executable/callable will be executed/called twice as well.