Strange inactive shard

hello,

I have 5 shards and 1 replica (default configuration)
2 nodes.

I delete the index, create the index and insert some data.
The problem is that sometimes 1 of shards is inactive.
Heppened 3 times.
If i restart one of the nodes (doesn't matter witch!), everything get synced and 5 shards are working.

<nabble_a href="elastic.png">elastic.png</nabble_a>

Exception trace:
<nabble_a href="trace.txt">trace.txt</nabble_a>

1st node java version 1.6.0_30
2nd node jave version 1.7.0_25
maybe different versions couse the problem ? Will try to reproduce it with version 7 on both nodes.

can't reproduce it with java version 7 on both servers