I suspect Wireshark activates the promiscuous mode of the network card and might help to migitate the problem.
Under Linux you can enable it by running
ifconfig eth0 promisc and disable it with
ifconfig eth0 -promisc.
In Windows, it's more complicated of course, but for some network card drivers there is an option in the network card hardware settings. I've also read that it might be possible on the command line, use
netsh bridge show adapter to find out the adapter number, then use
netsh bridge set adapter 1 forcecompatmode=enable (
1 to be replaced with the correct adapter number) to set "Forced compatibility mode" (apparently a Windows term for promiscuous mode) on that adapter.
You may also want to check for duplicate hardware MAC addresses on your network.