In pig9, can't have limit(order by) without getting a null error

a = load 'thing' as (x:int);
b = group a by x;
c = foreach b generate group as x, COUNT(a) as count;
d = limit (order c by count DESC) 2000;
describe d;

This gives the following error:

2011-12-13 13:56:32,144 [main] ERROR org.apache.pig.tools.grunt.Grunt - ERROR 1005: No plan for d to describe

In trunk, it ran without issue. Not sure what the difference is, but it'd be nice to patch 0.9.2 since a lot of people (including amazon!) are using pig 9 now.