This morning's lesson -- the XSLTListWebPart starts to break horribly in Designer as soon as you deviate from Microsoft's expected templates and patterns.

Case in point: as soon as you use multiple <xsl:template name=""> elements in the stylesheet, the Filter stops working. There's a caveat on that -- it works as long as you delimit the templates using the mode="" attribute and call them using <xsl:apply-templates> rather than <xsl:call-template name="">. So for example:

  <xsl:template match="/" >
    <xsl:variable name="Rows" select="/dsQueryResponse/Rows/Row" />
    <xsl:for-each select="$Rows">
      <xsl:call-template name="RowView" />
    </xsl:for-each>
  </xsl:template>

  <xsl:template name="RowView">
    <xsl:value-of select="@Title" /><br/>
  </xsl:template>

will then make the "Filter" button stop working in Designer, but using:

  <xsl:template match="/" >
    <xsl:variable name="Rows" select="/dsQueryResponse/Rows/Row" />
    <xsl:apply-templates select="$Rows" mode="RowView" />
  </xsl:template>

  <xsl:template match="Row" mode="RowView">
    <xsl:value-of select="@Title" /><br/>
  </xsl:template>

doesn't (despite producing an identical result).

[I♡SharePoint]