This is embarrasing.
0.4.0 apparently wasn't nearly as stable and tested as I thought - I did a full playthrough last night and found at least a dozen bugs, many of them relatively serious. As a stopgap measure until I get it fixed up to an acceptable level again, I've added a link above to the previous version, 0.3.2.
Note that mixing versions will cause problems - attempting to load a game saved in 0.4 will cause errors, including when the game attempts to automatically load last save you played with. If this happens, just click New or Load and load/start a new game, then save and refresh the page.