Strange ADF Problem, Timepart of a Date Lost

Today I have been working on an issue that has intrigued me for a while. One of our customer has an application (ADF BC - Struts w. JSP) that first inserts some data into an Oracle DB by creating a new row in the corresponding ViewObject, then fetches some additional data from another DB, and updates the newly created ViewObject with this data, however, this process has failed. While debugging this problem I noticed that one of the parts of the Primary Key was a Date column, and in the log files there were entries like:

oracle.jbo.RowAlreadyDeletedException: JBO-25019: Riga entit? della chiave oracle.jbo.Key[1 2006-12-27 aaa] non trovata in MyTable.

I also noticed the following a bit further down in the log:

06/12/27 12:22:31 [515] Original value :2006-12-27 12:22:28.0
06/12/27 12:22:31 [516] Target value :2006-12-27

so, it seems quite obvious why the error occurs, the only question now would be why. Now, I wanted to have the error messages in English, so I then added -Duser.lang=en_US, and restarted the Application. Obviously I expected to get the error messages in English, but instead, it worked fine. Strange... I hope to find some explanation for this...