different positions on different browsers

[xdude]

Not sure anybody has reported this - Since a few weeks ago, I've noticed that the same YSM ad on Yahoo would show up in different positions using IE versus Firefox. I contacted YSM and they only acknowledge the difference but offer no explanation.

It appears that the positions on IE reflect the real bid hierarchy. It's like there is some experimental shuffling of ad positions on Firefox based on some algorithm rather than mere bidding price. Does anybody observe similar discrepancies?