[Kenwood] 520S meter question

[Lou]

Hello all,

    I have a complete TS520S station and noticed something the other 
day.  When I am not using the xverters and the switch is off, on HF  I 
noticed that if I turn the six meter xverter on, the signal strength of 
the station will jump 3 s units.  In other words with the xverters off 
his report would be 53.  Same signal only with the xverter turned on 
(xverter switch on the back of the rig still off), the signal will jump 
to 58 which is what he sounds like, much higher than the 53.  I only 
notice this by turning on the 6 meter xverter.  No noticeable S meter 
deflection occurs when I turn on the 2 m xverter.  I am assuming it has 
something to do with the way you jump the two xverters but I don't 
understand why with the xverter switch off on the back of the rig why 
it  would have anything to do with my S meter on HF.  Any ideas?  Thanks
K8UPA