Reusing alias name in nested foreach causes incorrect results

The below script results in incorrect output for Pig 0.10 but runs fine with Pig 0.8,

input.txt
1	4
1	3
2	3
2	4

a = load 'input.txt' as (v1:int, v2:int);
b = group a by v1;
c = foreach b { x = a; x = order x by v2 asc; generate flatten(x); }
store c into 'c1';

Output from Pig 0.10
--------------------
1 4
1 3
2 3
2 4

Looking at the explain, it seems like the sorting is entirely missed out.
The script produces correct results if I change the alias name ie;

c = foreach b