Undo Option Lost After Event Macro Code

I have a sales spreadsheet, that people on this forum have very kindly helped me with by giving me two macros; one to remind users that they need to update the month cell when an order comes in, and the other to automatically put the date in a cell when any cell in that row is changed.

The final thread is here: Message To Remind That Cell Is Mandatory

and the Macro used is:


Private Sub Worksheet_Change(ByVal Target As Range)
Dim c As Range
Application.EnableEvents = False
For Each c In Target
If c.Column = 11 Then
If c.Value = "100 - Purchase Order In" Then
MsgBox "Is the Month In correct?"
End If
End If
If c.Column > 1 And c.Column < 18 Then
Cells(c.Row, 1) = Now
End If
Next c
Application.EnableEvents = True
End Sub

However...

We've now found that we cannot undo anything in these spreadsheets. If, for example, a cell is incorrectly copied or deleted, the only way of undoing the change is to shut down the spreadsheet without saving!

Is this just a by-product of using the time macro (a search on other threads suggests that it might be), and, if so, is there any way of changing it?