Again, sorry for the delay. Finishing grad school can be hectic.
I believe I have fixed this problem. The Scintilla editor only went missing if the XLua module was unloaded (e.g. all XLua-containing projects are closed), and then reloaded (when a new XLua-containing project is opened). If you closed MMF entirely, then everything would be okay the next time you opened it. It was a cleanup problem.
http://taloncrossing.com/xlua/xlua-dist.zip (Version 1.5.2)