We just found a major MacOS bug, but there seems to be no trace of it on the Web, so I am posting this here hoping that someone can help. We tested several machines and whenever you have an ethernet connection, trying to do an HTTP POST request with a sizeable load (such as editing a large article on wikipedia) will fail. This does not happen with WiFi, only ethernet (with a cable).
We tested with several browsers. Apparently, some version of Safari would not suffer from this bug, but I could not confirm it.
The problem is not hardware-bound because running Windows XP on the same machine fixes the issue. So, it seems there is a major bug in Apple’s ethernet driver.