iOS "PodCast" app fils up my phone; doesn't pre-download podcasts I want
If you go to a particular podcast settings, the options available are better described, and may explain the behavior you are seeing:

The option "Limit episodes" has a description that reads: 


  Limit the number of new episodes shown in the Unplayed view




Which does not appear to define how many episodes are downloaded but only how they are displayed.

This description is not present if you go to the app settings on the iOS Settings app.

On a separate setting you can choose to only download new episodes, all episodes or all unplayed. My guess is that marking "Only new" will help with your issue, but it depends on what is considered new by the app of course.