I wouldn't call it cool, haha... It's an eyesore to me. It only seems to happen with Asian rulers, (Tokugawa, Wang Kon, Qin Shi Huang, etc.) and only before the Industrial Era. Once it hits that era, everything is fine again.
The only thing that is modified is that I'm using Blue Marble and the BUG mod. I even completely uninstalled Civilization IV and reinstalled it again, and it still happens. I don't think it's my graphics card, but even if it was, I don't understand how that would cause it.
Does no one else have this problem? Also, river cottages seem less likely to float.