Cookie checksum error on OSX 10.7.5 && php 5.4.4

Problem of checksum :
substr($content, 0, strrpos($content, '¤') + 2)
return in the end of string '¤c'
must be '¤' only.
With my configuration it's need to be + 1 for the cursor position to be good, maybe a strrpos bug or '¤' length.