+1 for solving this… or at least making it very obviously documented and not a hidden “feature”.
Came here from Plex ignoring filename, shortening name of extra to single word, not even the first word of filenam? - #9 by biosehnsucht1
Ran into this with the extra from the Escape from New York movie titled “The Original Opening Bank Robbery Sequence (with optional commentary by John Carpenter and Kurt Russell)“ - after the cause was pointed out to me by @OttoKerner I renamed the file so instead of “Opening” (with capital ‘O’) it is “0pening” (with numeric zero) and that sort of badly works around the issue, but it’s less than ideal.
If anyone actually wants this “feature” then it should be off by default and opt-in. Either that or let us edit the metadata in Plex to fix it (movies you can’t edit any metadata of extras, unlike TV series’ “episodes”).