Description:
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I’ve found a bug in strtotime() function.
The present function does not return anything if you transmit unix_timestamp as a function parameter. However, if the last four digits of the value compose a valid year value, the function tries to calculate the whole date with the last 5 digits. Probably it fails there so it returns unix_timestamp the dates with the day and month equal to the current one, as far as the year goes, it is the one that the function has detected in the timestamp primary value. 

Example: 
Primary value: 1136412001 (January, 5, 2006)
On return: 998037401 (August, 17, 2001)

This way, a standard plug-in Smarty uses this function to transform the UNIX_TIMESTAMP format data into any data value. 
PHP Version 5.1.4

Original here: http://hcjack.livejournal.com/322438.html (on russian)