For what it's worth:
I ended up determining the if you assign a multi line string containing Chr(13) (carriage return) to a textbox.Text, the control replaces Chr(13) with Chr(13)Chr(10) (carriage return + linefeed). Since I was assigning the header/footer value from the .Text property I ended up with multiple lines.
My workaround was this:
Where remChr10 removes all linefeeds from a string and PageSetupXL4M comes from: http://www.mcgimpsey.com/excel/udfs/pagesetup.htmlCode:dim hl as string hl = remChr10(.text_header_left.Text) PageSetupXL4M LeftHead:=hl