After testing out the save file from ahrenjb: the good news is I managed to reproduce it - loading the save file twice in a row, it hangs on the second load.
The bad (well, sort of) news is that this is simply due to 512mb not being enough to both keep the current game in memory and load the new one; the loading process takes up a big chunk of memory. Raising the memory to 1024 seems to fix it, and looking at a heap dump, I don't see any indications of an actual memory leak, even after repeated reloads.
So, question: has anyone experienced other symptoms of a memory leak, such as the game's performance degrading after an extended play session? The crash-on-load (or simply failure to load), at least right now, looks like "not enough memory allocated" vs "actual leak".