It sounds like your disabling events somewhere when you close this book and
they remain disabled until the application is closed and re-opened. I suspect
you have other code somwhere in this book.
The example you gave with turning display alerts off may have been used; use
the activeworkbook.close savechanges:=true example instead. Take out the
application.displayalerts=false line. You can also use ThisWorkbook instead
of ActiveWorkbook to narrow it down to the workbook containing the macro.