Note that both leading and trailing spaces on your version numbers can break version_compare().
Tested on PHP 5.6.8:
<?php
echo "\nShould be 0";
echo "\n '1.0.0-pl' vs. '1.0.0-pl' ---> " . version_compare('1.0.0-pl', '1.0.0-pl');
echo "\n '1.0.0-pl' vs. ' 1.0.0-pl' ---> " . version_compare('1.0.0-pl', ' 1.0.0-pl');
echo "\n ' 1.0.0-pl' vs. '1.0.0-pl' ---> " . version_compare(' 1.0.0-pl', '1.0.0-pl');
echo "\n '1.0.0-pl' vs. '1.0.0-pl ' ---> " . version_compare('1.0.0-pl', '1.0.0-pl ');
echo "\n '1.0.0-pl ' vs. '1.0.0-pl' ---> " . version_compare('1.0.0-pl ', '1.0.0-pl');
echo "\n\nShould be 1";
echo "\n '1.1.1-pl' vs. '1.0.0-pl' ---> " . version_compare('1.1.1-pl', '1.0.0-pl');
echo "\n ' 1.1.1-pl' vs. '1.0.0-pl' ---> " . version_compare(' 1.1.1-pl', '1.0.0-pl');
echo "\n\nShould be -1";
echo "\n '1.0.0-pl' vs. '1.1.1-pl' ---> " . version_compare('1.0.0-pl', '1.1.1-pl');
echo "\n '1.0.0-pl' vs. ' 1.1.1-pl' ---> " . version_compare('1.0.0-pl', ' 1.1.1-pl');
