It's because the file for the 2nd link (the one with the larger gap) contains Unicode characters.
Open the page in Notepad - skim down and you'll see the
#posting_width div font looks different? Those are the Unicode encoded characters that are causing the glitch.
To fix things, go to File, Save As (but don't actually save it just yet) - you'll see the Encoding option set to UTF-8. Change it to ANSI and then save it again. You'll get a warning saying that you'll lose Unicode characters if you save as an ANSI file, but this is what you want to happen, so click OK.
Then open the new ANSI encoded file up again in Notepad and go back to the
#posting_width div. It's been converted but there will now be a question mark in front of the line, like this;
Remove the "?" and save again in ANSI mode and that should fix things (ie - narrow the gap).