BBB freezes when WiFi (UWN200 dongle) and Ethernet are used in parallel


in my project I need to use both WiFi and Ethernet interfaces on BBB.
If only one interface is plugged in BBB runs for days without problems. When both are connected BBB behaves unpredictably, freezes after few hours, or does not reboot properly without any error messages in logs.

For wireless I am using UWN200 dongle

When searching for a solution I found this tutorial at, where they state:
“(2) The Ethernet (RJ45) network cable must be removed when using the USB WiFi adapter.”

Does it seriously mean that only one network interface can be used on BBB? Are there some know HW/power issues (fixes)?
Is there some other WiFi adapter (preferably with antenna) someone could recommend?

I am using a high-end power adapter (3A).
Similar behavior is observed on different BBB revisions (A5C, A6, B)
Currently running Arch Linux, kernel 3.8.13-39 (but I have tried also other kernels without success).
The comment from logicsupply on unplugging the eth is related to Debian. Does it even make sense to try a different distro?