I believe the problem seems to be related to a lack of synchronization between the rendering engine (possibly the movement or physics code?), and the video card. The fact that the FPS clamp fixes the problem, tells me that it is not a videocard problem.
I'm almost certain that a real FPS cap in Oblivion (no, I'm not talking about vsync!!!) would solve the problem, but I still haven't found a mod that implements that, perhaps because it's something that can only be implemented at the renderer level. This would be like the setting "com_maxFPS" in Quake3. The Source engine (Half-Life2, Portal, etc.) also has a setting for a framerate cap.