It appears the Subject Titles for Forum Email Subscriptions vary in the wording for replies to the same thread. This causes havoc with the arrange by "Conversation" view of many email readers. Compare the highlighted subject to the others. Also, I have not quite figured the required new filter settings now that each forum has its own pseudo email address.
Another somewhat related issue, it appears I am receiving multiple email notifications of the same post. I am nearly positive this is the case as I have read a few threads today with only two posts; yet I have been linked to these same threads three or four times from email subscriptions.