Ok, it seems that some versions of PHP have a limitation of length of GET params:
Please note that PHP setups with the suhosin patch installed will have
a default limit of 512 characters for get parameters. Although bad
practice, most browsers (including IE) supports URLs up to around 2000
characters, while Apache has a default of 8000.To add support for long parameters with suhosin, add
suhosin.get.max_value_length = <limit>
inphp.ini
Source: http://www.php.net/manual/en/reserved.variables.get.php#101469