Out-of-memory on world creation in 13w02b

I'm getting out-of-memory errors whenever a new superflat world is being generated, or I teleport to a far-off location on an existing superflat world.

Not sure whether this is due to the long viewing range in superflat causing a lot of chunks to be generated, but it doesn't seem to happen in normal worlds.

Some chunks appear to get saved, and repeated loading of the partially generated world causes the region files to grow a bit further - but at no point does it become possible to play. The final crash report is attached.