Selecting a List item with an ItemRenderer immediately transitions back to unselected state

Question

I have a Spark List with a custom ItemRenderer. The ItemRenderer contains a custom component that is visible only when the ItemRenderer is in the selected state, e.g.:

<components:MyCustomThing id="customThing" left="158" top="22" includeIn="selected"/>

I've stripped down MyCustomThing to the bare essentials, namely:

<?xml version="1.0" encoding="utf-8"?>
<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009" 
         xmlns:s="library://ns.adobe.com/flex/spark" 
         xmlns:mx="library://ns.adobe.com/flex/mx">
</s:Group>

When selecting a list item with the ItemRenderer, the item transitions to the selected state as expected, but then immediately back to normal. If I change customThing to be included only in the normal state or both states, this problem does not occur. Even more perplexing, this doesn't happen consistently (probably 3 out of 4 times).

Any thoughts would be appreciated!