I am currently testing some features of the WordPress Plugin from: http://www.arnebrachhold.de/
The test was to see if the sitemap.xml send to Google would give an error on this childpage.
But the test ran fine, but I must state the I run the stable version 2.7.1. of the Plugin.
On live sites and Blogs I try to stay away from Beta versions, but thats me talking.
I sometimes work with new versions or even beta's if there are enough reasons to do so, like testing or if I am in need of some new features in that release.
The Open-SEF sitemap.xml generator for Joomla sites is running without problems in Google's webmaster central.
I Just released the file to Yahoo Site explorer, as a Feed option, where I send the sitemap.xml. The results on that one will take some time, like several days?