I have recently posted about how the autocomplete function in the versions since 3.62 has changed, and for the worse.  By searching the topic "autocomplete" on this forum, I see others have felt the same way.  I got a wonderful response from one of TB developers, Alexander Petrari.  His workaround - put in a single letter in the address book area of "handle" or nickname.  When you type that letter into the address field and then tab through, the email address will autocomplete.  It functions just as the older versions of TB did - one letter, tab through, no waiting, no need for 2 characters to be entered.
This was a major annoyance to me, and from what I see, others on this forum.  I am very pleased and really appreciate the response from the developers!