Moving an object is not smooth.. why?

Thanks Floyd I understand well your theory: it is a good point, but it does not fix my problem.

Let's try the following program

Graphics3D 640,480,32,2
SetBuffer BackBuffer()
camera=CreateCamera()
cube=CreateCube()
start% = MilliSecs()
While Not KeyDown(1)
ms% = MilliSecs() - start
z# = 13.0+ms/10000.0
PositionEntity cube,0,0,z
RenderWorld
Text 0,0,"Z pos     :"+z
Text 0,15,"Entity pos:"+EntityZ(cube)
Flip
Wend
End

You can see the value of EntityZ on the screen: it is changing smoothly, but the cube on the screen is only moving once per second...

I think it is an optimization of Blitz3D engine, but it is a problem for me because sometimes I have very slow moves and it looks crap.