Jira RSS 2.0 does not work with standard java parser (https://rome.dev.java.net/) since pubDate elements are incorrect.

RSS 2.0 was introduced in jira 3.7 (http://jira.atlassian.com/browse/JRA-9953), but it uses a non spec compliant format in the pubDate element.

The date of pattern <pubDate>Tue, 14 Aug 2007 14:21:22 +0200 (CEST)</pubDate>
is not a valid RSS 2.0 date since it must conform to http://asg.web.cmu.edu/rfc/rfc822.html#sec-5.1 dates.
These do not allow a trailing (CEST) marker. Rome also stops from adding any extra stuff to the date. From com.sun.syndication.io.impl.DateParser:

pp = new ParsePosition(0);
d = df.parse(sDate,pp);
if (pp.getIndex()!=sDate.length())

Since date is not formated correctly, jira RSS feeds are not possible to use in the portal.