Jitters during camera rotation, help?

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Hi there.

This is actually my first BB3D program (I've just come over from DBPro) and I've spent an hour searching the forums but I can't seem to solve this odd little problem.

Here is my code:
**********

timing = 1000/60

upkey = 200
downkey = 208
leftkey = 203
rightkey = 205

Graphics3D 1024,768,32,1 ; 1024x768, 32-bit, 1=fullscreen mode
SetBuffer BackBuffer()
camera1 = CreateCamera()
CameraRange camera1,0.1,1000
;AmbientLight 0,0,0

cube = CreateCube()
PositionEntity cube,0,0,10

light1 = CreateLight()

cubetexture = LoadTexture( "texture1.bmp" )
cubebrush = CreateBrush()
BrushTexture cubebrush,cubetexture
PaintMesh cube,cubebrush
Global camspeed = 1

;*****
While KeyDown(1) = 0

current = MilliSecs()

TurnEntity cube,0,1.0,0

If KeyDown(upkey) = 1 Then MoveEntity camera1,0,0,0.5
If KeyDown(downkey) = 1 Then MoveEntity camera1,0,0,-0.5
If KeyDown(leftkey) = 1 Then TurnEntity camera1,0,3,0
If KeyDown(rightkey) = 1 Then TurnEntity camera1,0,-3,0

Cls
RenderWorld

.time
finish = MilliSecs() - current
If finish >= timing Then Goto skip1 Else Goto time
.skip1

Flip

Wend
;*****

**********
What's happening is this: If I set the number on the first line to 1000/30 or 1000/45 or basically anything significantly different from 60 (desired fps) and if I get the camera close to my cube and then turn left or right, the cube "jitters". Specifically it appears to render twice in two different locations like the camera is rendering twice when I call flip or something.

Anyone have any idea what it is I've missed? I found several other posts with jitter issues but they didn't seem to help. And FYI my monitor's refresh rate is 85hertz not 60 so I don't think it's a refresh rate issue.

Any suggestions? Thanks in advance.