I’ve also been experiencing this issue. My podcast client is failing to update one of my podcast feeds with an error about an “unbounded prefix”.
It appears the problem is that the powerpress_rss2_ns() function doesn’t add an XML namespace for the podcast: prefix. This causes strict XML parsers to fail if any of the podcast: tags (e.g. <podcast:location>, <podcast:funding>, etc.) are included (hence, removing them fixes the problem).
