I suspect this may not even a DITA OT issue but possibly an Eclipse Help issue. Some issue with the search functionality?
When I generate output using the Eclipse Help deliverable from the same version of XMetaL Author Enterprise I get the following in the output HTML that is included with all the other files.
<html xml:lang="en-us" lang="en-us">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<meta name="copyright" content="(C) Copyright 2016"/>
<meta name="DC.rights.owner" content="(C) Copyright 2016"/>
<meta name="DC.Type" content="topic"/>
<meta name="DC.Title" content="Dog Leashes"/>
<meta name="abstract" content="Dog leashes allow you to maintain control over your dog's movements."/>
<meta name="description" content="Dog leashes allow you to maintain control over your dog's movements."/>
<meta name="DC.Format" content="XHTML"/>
<meta name="DC.Identifier" content="topic_FFBD2B97BF0A45099FCB2DCC08FE4A99"/>
<link rel="stylesheet" type="text/css" href="commonltr.css"/>
<main role="main"><article role="article" aria-labelledby="ariaid-title1">
<h1 class="title topictitle1" id="ariaid-title1">Dog Leashes</h1>
<div class="body"><p class="shortdesc">Dog leashes allow you to maintain control over your dog's
I'm not sure the specifics of how the Eclipse Help search feature works but it does not appear to need meta-data to be present to support searching, or at least I don't see anything in any of the other files the DITA OT is producing that would appear to be related to search and it is working but partially broken.
What happens if you modify the content to include additional text and then search for that instead of text appearing in the title?
What happens if you replace the occurrence of "Dog leashes" in the description with some other text and then search for "dog leashes"?
What happens if you search for "Dog leashes", vs "Dog Leashes", vs "dog leashes"? (case sensitivity?)
Perhaps that will provide some clues you can use to follow up.