Local Theme Songs not playing

Hi there. I use the latest Plex Version 2.4.37 on my iMac. I didn't know Plex before and I love it now.
But I noticed that when I place a "theme.mp3" audio file inside the main show directory, the theme does not play when the tv show was automatically identified before. So first I have to remove the identification, then the theme plays.
After this I correct the allocation so the detailed information from TheTVDB are assigned again. Then my own mp3 is used together with TheTVDB Info and Pictures.
Am I doing something wrong or is this a bug? How can I bring my own mp3 to work without this back and forth?
Thanks in advance for your help and reply.