Most likely, the page number goes to a default tab stop (because the TOC entry is "too short"). What you should do is explicitly add a right-aligned tab stop for the page number at the right margin. Also, be sure to clear any custom tab stops set before the end of the text in the affected entry. Doing this once would suffice, because the TOC styles are set to automatically update. See
http://www.word.mvps.org/faqs/format...CJasonTabs.htm.