After quite a bit of chasing, I’ve found at least one code error which is leading to the problem.
In powerpress.php, the internal configuration structure powerpress_feed is empty at the wrong time. Rather than being filled in with category-related information by powerpress_load_general_feed_settings(), it appears to be filled in with general post-type podcasting information (as if the first set of conditions checking for category had failed).
It is my conjecture that the powerpress_feed structure is being filled at the wrong time, perhaps even before the page parameters are being parsed. Thus, the category ID is not available when the condition is checked. The fields are clearly available later, and can be shown to be sufficient to satisfy the category conditions. For example, when they are checked within powerpress_rss2_head(), powerpress_feed is set up for post-type, but there are correct conditions for category type when you check is_category(), cat_ID, etc.
To test this, I simply reset the powerpress_feed to null before the (usually redundant) call to powerpress_is_podcast_feed() in powerpress_rss2_head(), and voila! The feed now contains the custom information for the category, whereas before it picked up minimal information (title only) from the category.
So, it *is* a code problem, and while I haven’t entirely solved it for you (the timing here is crude), it is somewhere around the first few calls of powerpress_is_podcast_feed().
I did notice that powerpress_is_custom_podcast_feed() also populates powerpress_feed, so there may be more than one occurrence of this timing issue.