Spellcheck should not highlight any words as misspelled until the cursor has advanced one character past the edge of the word. i.e. the spellchecker should not decide I have misspelled a word before I have finished typing the word.

For instance (using ^ to indicate the position the cursor is immediately in front of), in this scenario, the text appl is highlighted as misspelled:

appl
    ^

After typing the next character, the text is no longer misspelled:

apple
     ^

I recommend waiting until a space or punctuation has been typed to decide the word is misspelled:

appl 
     ^