Four part naming vs OPENQUERY permission difference?

Hi,

When connecting to a DB2 environment using the Microsoft OLE DB Provider for DB2, I sometimes run into permission issues:

• Using the OPENQUERY syntax, the query runs fine,
• Using the four part name syntax, I receive the following error message:

Msg 7357, Level 16, State 2, Line 1

Is security somehow applied differently between the two approaches? Or can someone give me another explanation for this behavior?