Why does my trendline equation change?

Posting the workbook won't work, it's 2.8 megs, plus there is confidential data contained there in.

Here is the code I use to generate the plot data and the trend lines. There is a routine above this code that searches about 200 columns of various depth looking for matches entered in a userform. The x and y data are stored in 2 strings, separated by commas. I have stepped through the code, and watched the chart as it's being generated. After the first series is created, the trend line is correct. After the 2nd series, the trend line changes to an altered equation. I have tried commenting out code to find out what is going on, but it has not yeilded anything.

    For iLooper = 0 To lbDate.ListCount - 1
        Application.StatusBar = " Generating Chart " & Int(((iLooper + 1) / (lbDate.ListCount)) * 100) & "% Complete"
        With ActiveChart.SeriesCollection.NewSeries
            If Not chkTrend Or lbDate.ListCount = 1 Then .Name = "=" + Chr(34) + lbDate.List(iLooper) + " Data" + Chr(34)
            .ChartType = xlXYScatter
            .Values = "={" + ArrAxisDataY(iLooper) + "}"
            .XValues = "={" + ArrAxisDataX(iLooper) + "}"
            If Not chkTrend Then
                .MarkerSize = 3
            Else
                .MarkerSize = 2
            End If
            .MarkerStyle = 8
        End With
        If chkTrend Then
            If lbDate.ListCount > 1 Then
                For iCount = 1 To ActiveChart.SeriesCollection(iLooper + 1).Points.Count
                    With ActiveChart.SeriesCollection(iLooper + 1).Points(iCount)
                        .Format.Fill.Solid
                        .MarkerBackgroundColor = rgbColor(iLooper)
                        .MarkerForegroundColor = rgbColor(iLooper)
                    End With
                Next iCount
            End If
            With ActiveChart.SeriesCollection(iLooper + 1).Trendlines.Add
                .Type = xlLinear
                .Name = "=" + Chr(34) + lbDate.List(iLooper) + " Trends" + Chr(34)
                .Border.LineStyle = xlContinuous
                .Border.Weight = xlThick
                .Border.Color = rgbColor(iLooper)
            End With
        End If
    Next iLooper