bug#34077: 27.0.50; icomplete, substring completion and C-x C-f misbehaving

[João Távora]

Hi maintainers,

I'm using substring completion, icomplete-mode and C-x C-f.  Navigating
deeper in directories using successive C-M-i's sometimes fails:
 
  Emacs -Q
  M-: (add-to-list 'completion-styles 'substring)
  M-x icomplete-mode
  C-x C-f p a t h / t o / e m a c s /
  s r c C-M-i
 
Expected to see the same as if I had typed "s r c /", instead I see
"{lib-src | src }".

This doesn't happen all the time: in this situation it seems to have
become confused by the fact that "lib-src" contains the substring "src"

João