genetics - What is the difference between copy number changes with and without allelic imbalance?

I require some clarification on copy number aberrations (structural gain and loss in chromosomes). From what I understand, gain/loss per se can be divided into two types.

Consider two alleles, A and B at the same locus on homologous chromosomes.

1. Allelic Balance: in one type of structural gain/loss, there is no resulting allelic imbalance; examples:

   
   
   
   • AB ==> AABB (duplication),
   
   
   • AB => -- (loss).
   
   



2. Allelic Imbalance: in the other type of structural gain/loss, there is resulting allelic imbalance; examples:

   
   
   
   • AB ==> AAB (duplication of A),
   
   
   • AB => -B (deletion LOH),
   
   
   • AB ==> BB (copy-neutral LOH).
   
   

First, is what I have described above correct?

Second, if it is correct, what is the biology underpinning these copy number aberration types? Are the mechanisms responsible for bringing about allelically-imbalanced CN change distinct from the mechanisms for bringing about allelically-balanced CN change? What are these mechanisms?

NB. I'm confining this to just copy number-related allelic imbalance.