Problem with Function grp.update

[manos@dynamitec]

Hello,

I am having a problem with the function grp.update in the latest firmware version. I am using the following script:

lux300 = grp.getvalue('0/6/3')
lux500 = grp.getvalue('0/7/3')
if lux300 == true then
 grp.write('5/0/3/', 300)
   os.sleep(0.2)
    grp.update('0/6/3', false)
    grp.update('0/7/3', false)
elseif lux500 == true then
 grp.write('5/0/3/', 500)
   os.sleep(0.2)
     grp.update('0/7/3', false)
     grp.update('0/6/3', false)
end

When the script is executed the G.A. 0/6/3 and 0/7/3 are sent to the knx bus and I just want to update the value internaly. 

What I am trying to do is to write two different values on the same G.A. when input G.A. 1 or 2 comes with ON on the knx bus. The two input G.A.s have the same tag so that whatever comes first to trigger the execution of the script. 

Is this correct or is there a better way to do it? And why is the grp.update function writes the value to the knx bus? 

Regards,