Shrinking list box

Never seen this before.
I have two option buttons, if I togle between the two, listbox1 height shrinks.
It will go from 108.7 to finally togling between 11.8 and 12.6.

Private Sub OptionButton1_Click()
ListBox1.Height = "108.7" 'force list box height? (for testing)
MsgBox ListBox1.Height 'for testing
    ListBox1.Clear

    TextBox11.Font = "Tahoma"
    SaveSetting "GdtFcfBuilder", "Variables", "sStdFont", OptionButton1.Value
    SaveSetting "GdtFcfBuilder", "Variables", "sIMSFont", OptionButton2.Value

    With ListBox1
        .Font.Name = "Tahoma"
        .Font.Size = "8"
        .AddItem "- (Straigtness)"
        .AddItem "Flat (Flatness)"
        .AddItem "Rnd (Roundness)"
        .AddItem "ProL (Profile Line)"
        .AddItem "ProS (Profile Surface)"
        .AddItem "Ang (Angularity)"
        .AddItem "// (Parallelism)"
        .AddItem "Per (Perpindicularity)"
        .AddItem "TP (True Position)"
        .AddItem "Con (concentricity)"
        .AddItem "Sym (Symetry)"
        .AddItem "CiRo (Circular Runout)"
        .AddItem "ToRo (Total Runout)"
    End With
End Sub

Private Sub OptionButton2_Click()
ListBox1.Height = "108.7" 'force list box height? (for testing)
MsgBox ListBox1.Height 'for testing
    ListBox1.Clear

    TextBox11.Font = "IMS"
    SaveSetting "GdtFcfBuilder", "Variables", "sStdFont", OptionButton1.Value
    SaveSetting "GdtFcfBuilder", "Variables", "sIMSFont", OptionButton2.Value

    With ListBox1
        .Font.Name = "IMS"
        .Font.Size = "8"
        .AddItem "³ (Straigtness)"
        .AddItem "ä (Flatness)"
        .AddItem "Î (Roundness)"
        .AddItem "ü (Profile Line)"
        .AddItem "æ (Profile Surface)"
        .AddItem "² (Angularity)"
        .AddItem "á (Parallelism)"
        .AddItem "ã (Perpindicularity)"
        .AddItem "û (True Position)"
        .AddItem "â (concentricity)"
        .AddItem "ÿ (Symetry)"
        .AddItem "ç (Circular Runout)"
        .AddItem "è (Total Runout)"
    End With
End Sub

Edit 1:
I added code to force the height, but when togling you can actually see the height change.
Is this due to changing Fonts?

Edit 2:
I set the Integral height to False, this seems to maintain the height but I cant scroll to the bottom of my list when option button2 is true.
So I am back to square one. I removed the following code form both option buttons:

ListBox1.Height = "108.7" 'force list box height? (for testing)
MsgBox ListBox1.Height 'for testing

Thus the listbox shrinks.

Any hints, tips or examples are appreciated.