Initially reported in the wiki page Internationalization (imported from MoinMoin in 2005):

One case where Unicode forces applications to deal with combining characters directly, rather than leave it to the browsers, is the alternate form of lowercase sigma at the end of a word. [...] auto-approval for case/accent-changing edits [...] needs to be handled.

Reference: https://en.wikipedia.org/wiki/Sigma

(Note that guess case tool already sets final/non-final sigma letters correctly.)