Deleting records on a subform while combo box is firing a not-in-list event

[OldEnough]

I have several forms that occasionally throw an error. The source of the error lies in a sequence of events the user does. I know what the sequence is but I haven't found a successful method for programming around it. Consider a form with 2 buttons "Save" and "Delete", with an associated sub form containing several fields, ItemID (Combobox), ItemDescription (Textbox), etc. The combo box on the sub form has a "not in list" event that opens a separate form for creating new items or clears the current field if the user has made a typo. The "Save Button" on the main form has code to save the details of data entered on the sub form. The "Delete Button" has code to discard the data in the sub form. The problem occurs when a user begins entering data in the ItemID combo box on the sub form, and while it is being edited but is not valid goes to the main form and selects "Delete". The Not In List Event fires on the combo box in the sub form and the code from the "Delete" button never executes. The current clumsy solution requires the user to select "Delete" 2 times in succession (when the not-in-list event has fired in the combo box), but I am hopeful that someone might suggest a better strategy. I would appreciate suggestions and ideas. It is enough of a nuisance that I am going to have to find a workaround.

[JeroenMioch]

I had to read your post about three times to get a picture of what the problem is and still i cant seem to grasp what your form and subform does.
To understand what the procedure is makes us better understand what you can do to prevent the problem from happening.
Can you start by making a screenshot (printscreen) and post that here so we can have a visual reference.

Especially the part of users making a new itemID or clearing the field when they made a typo makes me confused

[OldEnough]

The not-in-list event for the combo box on the sub form:
On Error Goto Error_CBOItemNIL
Dim ctl As Control
Set ctl = Me.cboItem

Dim Msg As String, CR As String
CR = Chr$(13)

If NewData = "" Then Exit Sub
Me.TxtNewData = NewData

Msg = "'Item Number " & NewData & "' is not in the list." & CR & CR
Msg = Msg & "Do you want to add it?"

'If the new data is correct then open the add Items form
If MsgBox(Msg, vbQuestion + vbYesNo) = vbYes Then
DoCmd.OpenForm "SA_frm_CEItem", , , , acAdd, acDialog, NewData
Response = acDataErrAdded
Else
ctl.Undo
Response = acDataErrContinue
End If

NormalClose:
Exit Sub
Error_cboItem_NIL:
MsgBox "Error # " & Err.Number & " " & Err.Description
Resume NormalClose
End Sub

The Code For the Delete Button on the Main Form:
On Error GoTo ErrorC

DoCmd.SetWarnings False
CurrentDb.Execute "DELETE * FROM tblBillDetTemp;", dbFailOnError
Forms!SA_frm_CEBill!sbfCEBill.Requery
DoCmd.SetWarnings True

Me.cboVendorID.SetFocus

NormalClose:
Exit Sub
ErrorC:
MsgBox "Cleanup Error. Error # " & Err.Number & " " & Err.Description
Resume NormalClose