As for the spell check issue, look for double spaces when using IE8.
I tested with Firefox 3.5.4 and IE8 on Win7. With Firefox I had no issues, with IE8 I could reproduce the error at will.
I used the following test words in my message:
The only difference is two spaces between two and th in the second example.
one two th <-- no error
one two th <-- error
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