Data vanish from potentials

Hi, please I need help on this.
One of our company CRM users detected that after editing data in potentials a field filled in with multipick list (our products) simply shows no previous data. User did not change that field but other one, and after saving changes our products field simply appears without data that there was jus a second ago. We solve it in an very costly way: filling in data again and again every whenever some potential is edited.
Thanks for all your support which means everything for companies as ours with no tech people.
Marko