Thanks Sarah, now i've found it (it was in a slightly different spot though, but hopefully the code is the same).
See if you can find this line of code:
string liveUrl = RequestContext.CurrentURL;
liveUrl = URLHelper.GetAbsoluteUrl(liveUrl);
Add two more line to it so it looks like this:
string liveUrl = RequestContext.CurrentURL;
liveUrl = URLHelper.GetAbsoluteUrl(liveUrl);
string token = "mkt_tok=" + URLHelper.GetUrlParameter(liveUrl, "mkt_tok");
liveUrl = liveUrl.Replace("?" + token + "&", "?").Replace("&" + token, "").Replace("?" + token, ""); // Handles removing JUST that parameter, without messing up other tokens.
Seems a little overkill, but this will remove JUST that token, in case other pages need the Urls (like bookmarking the 2nd page of a listing where ?page=2 is in the url and needed.
Tell me if that works!