problems adding to data while burning

Ok I have had success burning my first dvd film onto a 4.3gig dvd.
But when I try to burn data to a 4.3gig dvd after I have already added
data this is what happens.

1. First data is burning onto dvd (with the option,"allow more data to be added Later")

2. Finalising first data

3. Clicking burn second data onto. My first data has now been overwritten and only the second and final data is visible on the Disc.
so why did Nero lie to me after I clicked option "allow more data to be added Later"?

 

didnt nero say something along the lines about burning multi seesions that issues may arise.......

 

I have now been told u are not suppose to use multi session. I am now able to add data.