[otrs] admin system log size

Hi, I tried to configure the admin system log size to a value, different than the default one (4x1024). Tested on 1.2.2 and 1.3.1, giving the same error when opening the login window: Software error: Invalid argument at /opt/otrs/bin/cgi-bin/../../Kernel/System/Log.pm line 80. What is the reason for that? Is that a possible bug?