PrimaryKeys Collection Empty with OracleSchemaProvider

I want to generate bussines clasess implementing navegability. My database is Oracke 10g, and I´m using the OracleNativeSchemaProvider.

But when I want to iterate though the PrimaryKeys Collection of the table, this collection is always empty.

However, I test the same code with SQL Server 2005 and the SqlSchemaProvider and the code work fine.

The code section is this: 

<% foreach (TableKeySchema k in SourceTable.PrimaryKeys) {     %>
    <%= k.Name %>, <%= k.PrimaryKeyTable.Name %>, <%= k.ForeignKeyTable.Name %>
<% } %>

 I suspect a problem with the OracleNativeSchemaProvider. I want to know if exists a solution to this problem or if something wrong in my code.

Thanks for help.

vgutierrez