Test with @-sign like discussed on the user list.

src/tests/antunit/taskdefs/property-test.xml

@@ -150,4 +150,22 @@ b=$${a}
     <property file="${input}/x.properties" prefix="baz"/>
     <au:assertPropertyEquals name="baz.b" value="$${a}"/>
   </target>
+
+  <!-- 
+  Problems with @-sign discussed on the mailinglist.
+  Seems to work.
+  http://mail-archives.apache.org/mod_mbox/ant-user/201412.mbox/%3CCAPxjwW%2BQKFFj45O-ZbCGOnAkJXe9KJ5qKtVQCvS2x7hObRJmkQ%40mail.gmail.com%3E
+  -->
+  <target name="testAtSign">
+    <mkdir dir="${input}"/>
+    <echo file="${input}/x.properties"><![CDATA[
+once=@
+double=@@
+triple=@@@
+]]></echo>
+    <property file="${input}/x.properties"/>
+    <au:assertPropertyEquals name="once" value="@"/>
+    <au:assertPropertyEquals name="double" value="@@"/>
+    <au:assertPropertyEquals name="triple" value="@@@"/>
+  </target>
 </project>