SOLR 4.1 replication keeps downloading entire index from master

After upgrading to SOLR 4.1 replication keeps downloading entire index from master, hardware still the same.

I do not issue optimize on the master
The Merge factor is = 6
Tried both options in the useCompoundFile, same results.

Been looking at how files are updated in the master, I do:
http://host:port/solr/replication?command=indexversion

and the result is:

<response>
<lst name="responseHeader">
<int name="status">0</int>
<int name="QTime">0</int>
</lst>
<long name="indexversion">1361427997259</long>
<long name="generation">36967</long>
</response>

after a commit I see it changes to:

<response>
<lst name="responseHeader">
<int name="status">0</int>
<int name="QTime">0</int>
</lst>
<long name="indexversion">1361428018517</long>
<long name="generation">36968</long>
</response>

Any tips on how to further debug this?