Because your pattern 
/^(\d+)-(\d+)-(\d+) (\d+):(\d+):(\d+)$/

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doesn't match your data. Particularly the milliseconds.

Update: a pattern that matches the data you show is: 

/^(\d+)-(\d+)-(\d+) (\d+):(\d+):(\d+\.\d+)$/

[download]
Update 2: a pattern that matches with optional fractional seconds is: 
/^(\d+)-(\d+)-(\d+) (\d+):(\d+):([0-9.]+)$/

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In reply to Re: regex not working by trammell
in thread regex not working by gwhite

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