How to restrict variants in pricing for Configurable Material

Hi,

I have below problem , can some one help me to fix this issue.

1. Characteristic is created with single values for AD_DIFF , which can have SEL and ADP.

When Sales order is being created I can select either ADP or SEL , the problem is if I select ADP first and then Change this to SEL, System is determining variant pricing for both the selections.

Can some body help me to fix this issue ASAP.

Thanks,

Ananda