It has nothing to do with the Plexamp version, but with the server version:
(MUSIC) Changed played progress point for podcasts/long-form-audio to 99%, other audio content to 50% (12193)
Which means as soon as you tick this checkbox, this library is treated as a podcast/audiobook library.
I recommend you to create separate libraries anyway. It doesn’t make sense to suddenly hear a chapter of an adiobook if you simply trigger a “library radio” or somesuch.
