Comment 1 for bug 668878

I may have an idea. As a default, qBittorrent only considers one of the IP addresses (the first one it gets) assigned to a network address. Most recent Linux distributions have IPv6 enabled as a default. As a consequence, you probably have a IPv4 address and 2 IPv6 addresses assigned to wlan0. For some reason, qBittorrent might have used an IPv6 address.

First of all, are you using IPv4 or IPv6? If using IPv4, please try disabling the IPv6 support of your distro to see if it helps qBittorrent get the correct IP address.

Here is how to do it:

Debian / Ubuntu Linux

If you are using Debian/Ubuntu linux (thanks to beranger), open file /etc/modprobe.d/aliases
# vi /etc/modprobe.d/aliases

Find the line:
alias net-pf-10 ipv6

Replace with:
alias net-pf-10 off
alias ipv6 off