While running the TestUserAvatar using WebdriverBackedSelenium I noticed a number of errors in the test being caused by elements with duplicate IDs.

See the following snippet where id="comment_10020_header_fred" is duplicated:

<div class="action-details">
<a class="user-hover user-avatar" rel="fred" style="background-image:url(/jira/secure/useravatar?size=small&ownerId=fred&avatarId=10111);" id="comment_10020_header_fred" href="/jira/secure/ViewProfile.jspa?name=fred">Fred Normal</a>
added a comment - <span class=subText><span class=date>07/May/10 12:16 PM</span></span> </div>
<div class="action-body flooded">Fred's first comment! </div>
</div>
<div class="twixi-wrap concise actionContainer">
<a href="#" class="twixi"><span class="icon twixi-closed"><span>Show</span></span></a>
<div class="action-details flooded">

<a class="user-hover user-avatar" rel="fred" style="background-image:url(/jira/secure/useravatar?size=small&ownerId=fred&avatarId=10111);" id="comment_10020_header_fred" href="/jira/secure/ViewProfile.jspa?name=fred">Fred Normal</a>
added a comment - <span class=subText><span class=date>07/May/10 12:16 PM</span></span> Fred's first comment! </div>
</div>
</div>