Custom Fields Duplicate and Erased After first save

Hi, when I create a post and choose a new category and then deselect the default (uncategorized), there are 2 sections of the same Custom Fields, as if I had chosen 2 categories that had the same Custom Fields. After saving the post, the text that was inserted into the top Custom Fields is deleted (only dropdown content remain) and the second set of Custom Fields disapears. This is troubling, as I have to redo the work every time.

Can you please help?

Thanks,

Mauricio