Trouble grouping with for-each-group and sort

I have a collection of data that I'm trying to sort, but am having
difficulty with the for-each-group and sort operations.

The data is a series of elements of the form:

<DataItem xmlns="myns">
    <A>2</A>
    <B>1</B>
    <C>6</C>
    <D>4</D>
    <E>740</E>
    <F>99</F>
    <G>
        <sub1>202</sub1>
        <sub2>0</sub2>
        <sub3>
            <inner>1.1</inner>
        </sub3>
    </G>
    <H>
        <sub1>202</sub1>
        <sub2>262</sub2>
        <sub3>
            <inner>1.15</inner>
        </sub3>
    </H>
</DataItem>


where <G> and <H> have the same kind of data with the same sub-element
names.

The variable $list contains lots of DataItem elements.

Here's my current grouping and sorting attempt (from a larger
transformation):

    <xsl:for-each-group select="$list/myns:DataItem" group-by="myns:A">
        <xsl:sort select="current-grouping-key()" data-type="number"/>

        <xsl:for-each-group select="current-group()" group-by="myns:B">
            <xsl:sort select="current-grouping-key()"
data-type="number"/>

            <xsl:for-each-group select="current-group()"
group-by="myns:C">
                <xsl:sort select="current-grouping-key()"
data-type="number"/>

                <xsl:for-each-group select="current-group()"
group-by="myns:D">
                    <xsl:sort select="current-grouping-key()"/>

                    <xsl:for-each-group select="current-group()"
group-by="myns:E">
                        <xsl:sort select="current-grouping-key()"
data-type="number"/>
                        <xsl:sort select="myns:G/myns:sub3/myns:inner"
data-type="number"/>

                        <xsl:call-template name="process-data" >
                            <xsl:with-param name="data-set"
select="current-group()"/>
                        </xsl:call-template>

                    </xsl:for-each-group>
                </xsl:for-each-group>
            </xsl:for-each-group>
        </xsl:for-each-group>
    </xsl:for-each-group>


When I run the transformation, all the groupings from the
for-each-group operations work fine. but the data is not sorted (it
appears) at the innermost grouping according to the value of
"myns:G/myns:sub3/myns:inner" when the "process-data" template is
invoked.

All the other data is grouped and sorted fine, except for the last
sort on "inner".

Any ideas why the last sort doesn't appear to work?

Does a data-type of "number" for sorting correctly process numbers
with decimal points?

Am I using the wrong select on the parameter for process-data?

Is current-group() at that point not the sorted data that I think it
should be?

Is there a limit on nested for-each-group operations?

I'm using Oxygen 10.3 with Saxon SA 9.1.0.7.

Thanks, Mike

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