CC detects one modification twice

hi all,

First, prese forgive me if this is well known issue. I'm quite new to using
CruiseControl.

If my server's clock is losing several minutes, CC detects a modification
twice in a file which is modified once.
It means CC starts two builds at the same time, and both of them never
scusses!!
CC detect "modification in the future" at first polling.
But in next polling, CC detect "one modification" again in the same file.
I have no idea what "modification in the future" means. What is happening!!
But I gess CC has it's own clock and it is not synchronized with my
serever's one.
Because if my server's clock is ticking accurately, CC detects just one
modification.
                                                                            
                                                                            
                                                                            

I want to make syure that if CC has it's own clock or not.
And if CC has, How can I ajust it?
And if CC don't have, why dose CC detects a modification twice?

I realy thank you for your help and reading my miserable English.
                                                                            
                                                                            
                                                                            


---------------modificationset---------------
    <modificationset quietperiod="0">
        <filesystem folder="${autobuild.project_root}/SrcUpdate.tag"/>
    </modificationset>


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