Bug: Background music not saving in "Update Series" menu (especially for larger files)

User reports that custom background music (.mp3) uploaded via the Series Edit menu (Series -> Eye Icon -> Edit) does not save when clicking "Update Series", even though the filename is displayed before saving. Interestingly, the same files (some > 5MB) work perfectly when uploaded to individual videos via the manual editor. This indicates a bug specifically in the series-level update functionality or an undocumented file size limit for that specific menu. User wants the software checked.