VariableSizeCommunication hangs

Blocks: !411 (merged).

When run with four ranks, VariableSizeCommunication seems to have a tendency to hang.

================== variable size =======================
2: Gathering 1 entries for index 66666
2: Gathering 2 entries for index 66667
1: Gathering 3 entries for index 33333
1: Gathering 1 entries for index 66666
0: Gathering 3 entries for index 33333
1: Gathering 2 entries for index 66667
2: Scattering 1 entries for 66666: 66666 
1: Scattering 1 entries for 66666: 66666 
2: Scattering 2 entries for 66667: 66667 66668 
1: Scattering 2 entries for 66667: 66667 66668 
0: Scattering 3 entries for 33333: 33333 33334 33335 
1: Scattering 3 entries for 33333: 33333 33334 33335 
0: Gathering 4 entries for index 33334
1: Scattering 4 entries for 33334: 33334 33335 33336 33337 

Compilation exited abnormally with code 1 at Wed Nov 29 15:59:14

It is intended that rank 3 does not participate in the communication.

Full log.txt