Find this around line 470 of checkout.aspx.vb (root):
        If numMinOrderValue > 0 Then
            If GetKartConfig("general.tax.pricesinctax") = "y" Then
                'Prices include tax
                If UC_BasketView.GetBasket.TotalIncTax < numMinOrderValue Then
                    Response.Redirect("~/Basket.aspx?error=minimum")
                End If
            Else
                If UC_BasketView.GetBasket.TotalExTax < numMinOrderValue Then
                    Response.Redirect("~/Basket.aspx?error=minimum")
                End If
            End If
        End If
change to
        If numMinOrderValue > 0 Then
            If GetKartConfig("general.tax.pricesinctax") = "y" Then
                'Prices include tax
                If UC_BasketView.GetBasket.TotalIncTax < CurrenciesBLL.ConvertCurrency(Session("CUR_ID"), numMinOrderValue) Then
                    Response.Redirect("~/Basket.aspx?error=minimum")
                End If
            Else
                If UC_BasketView.GetBasket.TotalExTax < CurrenciesBLL.ConvertCurrency(Session("CUR_ID"), numMinOrderValue) Then
                    Response.Redirect("~/Basket.aspx?error=minimum")
                End If
            End If
        End If
This applies the present currency to the minorderval setting, so changing currency should see the min order value increased by the same amount in numeric terms as the order total						
			    
				
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