Now that you have traced it to an issue with addons / plugins / extensions, perhaps so more vigorous testing by disabling these various products might help identify the specific culprit. Knowing the specific offender might help us with some additional testing to perhaps duplicate the issue. I for one would be willing to install the specific product into whichever browser and test myself. I could then forward the information to Mike who could coordinate with the vBulletin development team to see if that is something they can or would be willing to address.
Thanks
Randy
EIIT: Also it would be nice to know specifically in reference to Chrome, which version you are using? Are you using that latest stable build or chasing the seemingly endless beta versions?