Replace group in Regex function mode

[lindlind]

I have the following string:

<span class="line">Come here, he says.<span aria-label="11" class="page-normal" id="d5e1496" role="doc-pagebreak" title="11" epub:type="pagebreak"></span></span><br />

If I do a search and replace in Regex mode like this:

Search:

<span([^>]*"pagebreak"> ?)</span>

Replace:

<xxspan\1</xxspan>

The result is:

<span class="line">Come here, he says.<xxspan aria-label="11" class="page-normal" id="d5e1496" role="doc-pagebreak" title="11" epub:type="pagebreak"></xxspan></span><br />

However, if I add the following in a Regex-function:

return regex.sub('<span([^>]*"pagebreak"> ?)</span>', '<xxspan\1</xxspan>', match.group())

The result is this:

<span class="line">Come here, he says.<xxspan
</xxspan></span><br />

What am I doing wrong here?