Why does spell check skip the lower case letter "i"

[Coach]

Every time spell check runs it misses a single lower case letter. For instance if i type this line the lower case i is not marked as mis-spelled.

I have corrected this by setting the auto-correct rule of "i" to "I".

The problem I cannot correct is if I type a single letter other than I it does not mark or stop with spell check.

If I type o my it does not mark/flag as mis-spelled.
If I type s this letter or any other constant it is not marked/flagged as mis-spelled.

Any thoughts on a resolution would be greatly appreciated.
Thanks in advance.