After upgrading, I ran into two issues.
1. Upon first accessing the admin page after upgrading, it was showing HTTP Error 500: Internal Server Error. Phplist’s troubleshooting document tells how to correct that problem:
HTTP Error 500: Internal Server Error – The server encountered an internal error or misconfiguration and was unable to complete your request. This error message may have different causes. If you get a “500 Server Error” when installing, your server is probably running PHP as a cgi, not as an Apache module (also known as phpsuexec). Solution: In /lists/.htaccess, find php_flag magic_quotes_gpc on and delete or comment out (with a #) this line. (However phpList may display “Warning: Things will work better when PHP magic_quotes_gpc = on” which is addressed below)
2. On the Send a Message screen, the editor field was missing – in fact everything below the tabs was gone! I found a fix in the phplist forums. Specifically, just removing the comments from line 1034 wasn’t enough. Replacing lines 1031 – 1042 with the following, as recommended, fixed it.
$maincontent .= '