I am posting this comment in the probably vain hope that it will generate attention from Adobe - I have used DW since version 1 and the spell checker seen little if any improvement and it remains very poor and buggy. A main reason for using a visual editor is if you have lots of text on your site. Even if you copy and paste from a text editor like Word there are the inevitable times that spell checking a document is critical. The DW spell checker is simply unreliable and makes many errors. It is unacceptable to have such a poor quality tool in an application that is so expensive. I hope that Adobe will take this issue seriously and devote some resources to fixing it.
I'm afraid you won't get any attention from Adobe posting here.
The official channel for a bug report is here:
Can you provide some specific steps which everyone can follow to clearly reproduce the issues you're facing? That's the best way to file a Bug Report.