Over the past weekend we upgraded from version 6.0.5 to 6.0.6, specifically to address bug 42010 as well as some other issues with HTML composing when using IE. The upgrade appears to have fixed the HTML composing issues, but unfortunately a new bug with Text Mode composing when using IE appears to have surfaced.
When composing your first new message all appears OK. However when composing any subsequent messages the cursor starts in the message body, instead of the "To:" field. This only seems to happen with IE (I've tested Firefox and Chrome) when you are not using the "Compose in new window setting".
I just wanted to bring this to others attention in case they others are running into the same issue. I know I recommended that my users switch to Text Mode while we were dealing with the HTML compose mode issues, so now I've got several users running into this issue. I've created bug 46439 (hopefully not a duplicate) to address this issue.