This may be related to all the issues surrounding TMDB and the no-title posters but a whole bunch of tv series (non-english) have all gone screwed up with my collection. They used to be fine, but alas no longer.
They are all named correctly (or rather nothing has changed in names/folder structures and some are from 2010) - Example: series name: BORGEN Folder name BORGEN inside folders Season 1 Season 2 etc and filenames Borgen S01E0x - three of the seasons display a proper poster, the fourth a generic black with orange clapperboard and the main series poster is either white or black/orange clapperboard.
Many more series (all “foreign” language) are broken like this.