I am not real good with macros. If I was dealing with the issue, I would use VBA to open the form. Before the VBA executed to open the second form, I would save the current record within the first form.
Code:
If Me.Dirty = True Then
Me.Dirty = False
End If
This may be enough. However, I typically add additional saves from the second form.
Code:
If Me.Dirty = True Then
Me.Dirty = False
End If
'Save the first form, too
If Forms!FirstFormName.Dirty = True Then
Forms!FirstFormName.Dirty = False
End If