I'm not sure if there's anyone (or how many) who use NeoLemmix but don't follow the bug reports subforums, so just in case, Nepster has made an experimental update with many bug fixes. Please check it out, as many of these are likely to be adopted if there's no problem with them.
http://www.lemmingsforums.net/index.php?topic=2626.msg57149#msg57149