Is the field for the popup menu a global field? I don't think that it is and thus you see data in the header from a different record than the one that you originally modified when you selected a value from the pop up men. It would seem specifying a global storage option for this field would resolve the immediate issue.
Note: When you put a non global field in the header or footer of a layout, in Browse mode, you will see data in that field from which ever record is current. Simply clicking on different records on the layout can cause different data to appear in such a field. But in Preview Mode or when printing from the layout, the header will show data from the first record on a given page and the footer will show data from the last record on a given page.
You may also find the scripted find examples used here to be of interest: Scripted Find Examples
Absolutely fixed the problem. Typically the simplest solutions get overlooked. Thank you for your help.