Multiple <value> elements in a single item

System

I have a DCT with a bunch of items inside two containers, of which three are not required. There are no replicants in the template. Twice today when a DCR has been saved the XML has contained multiple <value> tags for a single item. I have only seen this happen for items that are not required. The relevant section of the DCR looks something like:

...
<item name="Data">
<value>
<item name="PolicyName">
<value/>
</item>
<item name="PolicyBody">
<value/>
<value/>
</item>
</value>
</item>
...

The second <value /> element inside PolicyBody is the problem. This doesn't seem to bother the templating engine at all (although since there are no values I am not sure which it would show me in the form), but when my XPath tries to find the value of PolicyBody it throws an exception because there are multiple values.

Does anyone know what causes this?