Order of bars in bar chart can't be changed

Hi,
I'm totally puzzled why a simple task as this one, doesn't do as expected.

I have this bar chart showing sum(invoiceamount) on x and invoicedate/month on y. For some obscure reason the default order of y is by amount of x:

But I'd like the order to be by year/month.
So, as I've done before, I exported the xml and made this alteration by adding the red part:

<Visualizations>
<visualization>
<savedqueryvisualizationid>{188E55C3-4753-E211-A108-00155D01688C}</savedqueryvisualizationid>
<datadescription>
<datadefinition>
<fetchcollection>
<fetch mapping="logical" aggregate="true">
<entity name="invoice">
<attribute groupby="true" alias="_CRMAutoGen_groupby_column_Num_0" name="psa_approvedon" dategrouping="month" />
<attribute alias="_CRMAutoGen_aggregate_column_Num_0" name="totallineitemamount_base" aggregate="sum" />
<order alias="_CRMAutoGen_groupby_column_Num_0" descending="false" />
</entity>
</fetch>
</fetchcollection>

Repack, import, publish, but no change whatsoever. I did do the checks (a thousand times by now) if I'm looking at the right chart, but really, that's OK.

Any idea what I'm overseeing here?

Thanks in advance,
Regards,
Jeroen