I cannot reproduce that. Steps I tried:
1) Paste: <p id="filepos2207" class="calibre1"><span class="calibre2"><span class="bold">Chapter One</span></span></p> into an html file
2) Paste: <p([^>]*>\s*(<[^/].+?>)*Chapter.+?</)p>
into the find box and set mode to regex and search in current file
3) Click Find, the tag from (1) is highlighted