Heap Size Current decreases (-Xms1024m seems to be ignored)

Hello,

I have a strange behaviour under BEA Weblogic 9.1.

I startup a managed server with the java argument settings:

-server -XX:MaxPermSize=256m -Xms1024m -Xmx1024m
-Dcom.sun.xml.namespace.QName.useCompatibleSerialVersionUID=1.0

and the server startup normally.

Unfortunetelly in the Console and also with reading the JVM memory parameter via
WLST the "Heap Size Current" changes its value to lower values than
1024MB even if I set -Xms1024m.
Over the time "Heap Size Current" changes it's values again &
again (Decreases).

How could it be ? 
How can I force BEA and/or Java to set -Xms1024m fixed ?

Thx a lot.

My environment is:

WebLogic Temporary Patch for CR325828 Fri Jun 15 15:00:10 EDT 2007 
WebLogic Temporary Patch for CR295567 Tue Feb 27 16:15:17 2007 
WebLogic Temporary Patch for CR294046 Tue Feb 6 14:12:55 2007 
WebLogic Temporary Patch for CR282546 Fri Jun 23 11:55:52 2006 
WebLogic Temporary Patch for CR279247 Wed Jul 26 18:27:09 2006 
WebLogic Temporary Patch for CR276583 Mon Oct 30 17:54:17 2006 
WebLogic Temporary Patch for CR275126 Thu Mar 1 11:20:01 2007 
WebLogic Temporary Patch for CR274588 Wed Jan 10 13:53:36 2007 
WebLogic Temporary Patch for CR266413 Mon Jan 22 11:05:38 2007 
WebLogic Temporary Patch for CR265150 Fri Oct 27 17:56:04 2006 
WebLogic Temporary Patch for CR265510 Tue May 2 14:20:56 2006 
WebLogic Temporary Patch for CR258305 Fri Sep 29 15:27:33 2006 
WebLogic Temporary Patch for CR237973 Fri Sep 29 17:14:39 2006 
WebLogic Temporary Patch for CR236939 Tue May 30 15:19:32 2006 
WebLogic Temporary Patch for CR220886 Wed Feb 28 23:36:02 2007 
WebLogic Temporary Patch for CR218580 Fri Mar 23 12:09:15 2007 
WebLogic Server 9.1 Mon Dec 12 19:26:33 EST 2005 689178
 
Java Version: 1.5.0.10
Java Vendor: Hewlett-Packard Company

Server OS = HP-UX  B.11.11 PA-RISC

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