Combo Box Selection Changes w/o Input

Hello

I've got two combo boxes that work with each other. The first allows the
user to select a pricing matrix group (there are 5 total) and the second
allows the user to select a contract term (each group has unique terms) which
selects the appropriate pricing matrix. The problem I am encountering is
that when I've made changes to the workbook (e.g., adding a new worksheet or
when the autorecover function runs) the second combo box reverts to a blank
and the pricing is lost. This requires the user to reenter the contract term
to get the pricing back. I can't figure out why its happening.

Here is my code (abbreviated ...) :

Private Sub ComboBox1_Change()
If ComboBox1.Value = "GroupA" Then
ComboBox2.Value = ""
ComboBox2.ListFillRange = "GroupA_Terms"
End If
If ComboBox1.Value = "GroupB" Then
ComboBox2.ListFillRange = "GroupB_Terms"
End If
....

End Sub

Private Sub ComboBox2_Change()
If ComboBox1.Value = "GroupA" Then
Sheets("Rates").Range("GroupA_Matrix").Copy
Sheets("Assumptions").Range("A29").PasteSpecial Paste:=xlPasteValues,
Transpose:=False
Application.CutCopyMode = False
....
End Sub

If I remove the ... ComboBox2.Value = "" ... line I don't have the problem.
However, if the user switches the ComboBox1 value, the term doesn't change
until they select a new one. This results in error messages as the formulas
can't find the term they have selected.

Any thoughts?