When a message with relatively short Japanese subject is received, the subject is shown as undecoded entity reference (&#<5-digit num>). Placing the mouse cursor over the subject line in the Message Audit Log entry shows the expected / decoded characters in the mouseover.
Short Subject lines are not being encoded properly for display in some product localizations. The correct subject line data is stored internally and can be reported on but is not being displayed correctly in all cases.
This issue has been addressed with the SMG 10.6.3 release.
As this is a display issue, for other versions there is no workaround other than to view the Subject line using the mouseover tooltip.