DataFormWebPart: Sorting with Last modified bug

Question

I have created a DataFormWebPart with SPD2013. In my DataFormWebPart, I sort the table by Modifed column. The column is display with follow format:
<xsl:value-of select="ddwrt:FormatDate(string(@Modified), 2057, 5)"/>
However, when sorting with descending order. The time at 12:xx is at higher proirity:
24/04/2015 12:44
24/04/2015 12:25
24/04/2015 17:18
24/04/2015 16:55
24/04/2015 15:52
Why is that? Can we fix it? Thank you.

Answer 1

Thank you for your reply. I have done more test. When I press F5 to refresh the page, the sorting order is correct. However when click on the column header to sort the order is incorrect.
There are only two sentense start with <xsl:sort
<xsl:sort select="*[name() = $dvt_sortfield] | @*[name() = $dvt_sortfield] | text()[name(ancestor::*[1]) = $dvt_sortfield]" order="{$dvt_sortdir}" data-type="{$dvt_sorttype}" />
<xsl:sort select="ddwrt:FormatDate(string(@Modified),2057,5)" order="descending" />
and here is part of column with wrong order when clicking the header:
<xsl:call-template name="dvt.headerfield" ddwrt:atomic="1" xmlns:ddwrt="http://schemas.microsoft.com/WebParts/v2/DataView/runtime">
 <xsl:with-param name="fieldname">@Modified</xsl:with-param>
 <xsl:with-param name="fieldtitle">修改時間</xsl:with-param>
 <xsl:with-param name="displayname">修改時間</xsl:with-param>
 <xsl:with-param name="sortable">1</xsl:with-param>
 <xsl:with-param name="fieldtype">x:dateTime</xsl:with-param>
</xsl:call-template>
Here is how the sorting looks like:
24/04/2015 15:52
24/04/2015 16:55
24/04/2015 12:44
27/04/2015 13:49
27/04/2015 13:53