I generate some Excel files from c#

I turn change tracking on, which requires me to share the the
document. So I save with sharing, turn change tracking on, save again,
then make the excel application Visible.

Everything seems to work fine. Change tracking works, things seem ok

I close Excel, then open the file up manually. Change tracking doesn't
show all changes, for some reason it's set to "Since I last saved"

huh?

my code
excelApp.Workbooks[1].KeepChangeHistory = true;

object oWho = "Everyone";
excelApp.Workbooks[1].HighlightChangesOptions(Excel.XlHighlightChangesT ime.xlAllChanges,
oWho, Type.Missing);
excelApp.Workbooks[1].ListChangesOnNewSheet = false;
excelApp.Workbooks[1].HighlightChangesOnScreen = true;


any ideas?

thanks
mike