Problems with Full description in PO

Hi, I have a little problems when I open a PO the items only show a code

Then, I press F5 and the item shows the full description.

Why? I need see the full description always!

I am on Version 8.4.3 and confirm the same behavior. I would like to add that the first time opening the purchase order doc, the full description does show. On the second document, only the item code is showing. F5 will cause the description to reappear.