Long POST parameter is truncated

We are sending uploaded file (image,pdf, etc) to the server to be saved in the database.
The file is Base64 encoded and sent as XML field, i.e.

<?xml version="1.0" ?>
 <Request>
  <Binary_File>R0lGODlhkA....long Base64 string....s=</Binary_File>
</Request>

While sending this XML as POST parameter it's truncated,
i.e. when we get the parameter in the HttpServletRequest.getParameter method the result looks like this:

<?xml version="1.0" ?>
<Request>
  <Binary_File>R0lGODlhkA....long Base64 string...9g0l1Pv9/n8

Exactly the same problem occurs on WildFly 8.0.0.Final and WildFly 8.1.0.Final and never on JBoss5.

It’s looks like the problem is related to timing: on our development server the problem to success ratio is ~ 14/6. When we run apache and mod_jk in debug mode the ratio was swapped, i.e. 14 successful / 6 failed requests. On production servers almost all of the requests failed (even with apache and mod_jk debug mode enabled).

Output of the mod_jk (saved as TCP dump) for both successful and failed request is exactly the same.

When comparing the successful and failed data received by server (server_dump_OK.txt and server_dump_ERROR.txt) we see that in failed case the block before the last one is inserted twice, i.e. in success we see blockX+last block; in failed – blockX+blockX.