Beats the heck out of me! That usually means there's an extra blank line been added to the php file during an edit, but you're not editing the file.
Does it happen if you don't change anything but merely edit and then hit the update button?
And secondly can you be a bit more explicit on EXACTLY what is being changed. Perhaps the field length is being exceeded?
I've just an edit on a system , changing rates, without any problem, so it doesn't seem to be 'generic'