BALANCESHARDUNIQUE does not distribute properties correctly

Create a collection of 8 slices on 4 nodes, 2 replicas of each slice.

Node IP is:
192.168.182.246:21101
192.168.182.247:21104
192.168.182.248:21101
192.168.182.149:21104

After executing the BALANCESHARDUNIQUE command, the leader node is balanced as follows:
Cloud Graph (* Leader)
shard1 |- * 192.168.182.248:21101

shard2 |- * 192.168.182.249:21104

shard3 |- 192.168.182.247:21104

shard4 |- 192.168.182.248:21101

shard5 |- 192.168.182.249:21104

shard6 |- * 192.168.182.248:21101

shard7 |- 192.168.182.248:21101

shard8 |- * 192.168.182.247:21104

The correct expected result should be that there are two leader on each node.

But the actual result is..
there are 3 leaders on 192.168.182.249:21104,
and only one Leader on 192.168.182.247:21104
the others are distributed correctly.