I met a very "strange" behavior of VBA with Fillet Command send via ThisDrawing.SendCommand function.
I have the function Fillet_2Line (line1, line2, r), which will apply the Fillet command to line1, line2 with Radius=R
Code:
Sub fillet_2line(line1 As Variant, line2 As Variant, radius As Double)
    Dim text As String
    text = "f" & vbCr & "r" & vbCr & radius & vbCr & "(handent " & Chr(34) & line1.Handle & Chr(34) & ")" & vbCr & "(handent " & Chr(34) & line2.Handle & Chr(34) & ")" & vbCr
    ThisDrawing.SendCommand (text)
End Sub
As you can see, the function is very simple, call Fillet command from Autocad then select two lines by their handle. Use can reproduce the function without VBA by call Fillet command and select two POLILINES by their HANDLE.
However, it works on LINE, but NOT POLYLINE. If I select two polylines by left click on them, it works. But if I select two polylines by their HANDLE, it does not work!
Fillet 2 Line - Selected by left click - Works
Fillet 2 Line - Selected by handle - Works
Fillet 2 PLine - Selected left click - Works
Fillet 2 PLine - Selected by handle - Does not workUntitled.jpg