Take the word "commissioner".
If you miss out one of the "m"s, the spelling checker recognises that "comissioner" is wrong, and suggests the correct word.
If you miss out one of the "s"s, the spelling checker recognises that "commisioner" is wrong, but is unable to find a suggestion....
If you miss out one of the "m"s, the spelling checker recognises that "comissioner" is wrong, and suggests the correct word.
If you miss out one of the "s"s, the spelling checker recognises that "commisioner" is wrong, but is unable to find a suggestion....