Well, okay what you get is definitely not what podPress should give you.
But the question is why you get such a XML output. I have done a few first tests and followed the steps you have done. So far I have no trouble to customize the feed title, itunes:subtitle and itunes:summary. If you leave the category description empty and choose Use Category Description then this feed gets automatically the description of the default feeds. That is that way a long time. But maybe it is worth to change that behaviour. But that is probably not the big problem.
There is one very interesting thing in the output you have posted above:
There is no way that this is a tag which podPress has added to the feed.
It is possible that podPress inserts an empty
<itunes:subtitle> tag but - and this is maybe a bug - not in this good style of an empty XML element. (the ouput of podPress would be
Somehow this output is not the direct output of podPress.
Please, make sure that there is no other plugin caching or interfering in any other way with the feed - at least during your tests.
But it is not impossible that the software which you use to view the XML has displayed the subtitle tag this way.
Maybe use Firefox to view this feed. Right-click and use View source code to view the XML of the feed. Maybe the software you are using streamlines the code.
I will make some further tests too.