Our software outputs some xml and a client has another company loading this xml into some data warehouse and doing reporting on it. The other company are saying we are outputting duplicate records in the data.

I look and see something like this:
<foo name="test">
<bar value="2" />
<bar value="3" />
</foo>

They say there are two foo records with the name test..
We ask them to send the xml file they are looking at. They send an xlsx (Excel!) file which looks like this:

name value
test 2
test 3

We try asking them how they get xlsx from the xml but they just come back to our client asking to find what we changed because it was working before. Well we didn't change anything. This foo has two bar inside it which is valid data and valid xml. If you cant read xml just say so and we can output another format!