MinimServer (0.8.3f, Raspbian) not discovered by BubbleUPnP when VPN is on

[brencer]

When I start Minimserver on my Raspbian (Raspberry Pi 2 model b) without using a VPN, everything works swell with my tablet and phone (using BubbleUPnP on both). The server is discovered and everything plays. But when connected to a VPN (I'm using AirVPN with it's own software, which, as far as I understand, uses OpenVPN system - don't know any more technical details about that) neither of my mobile devices can find Minimserver any more. Closing and restarting Minimserver doesn't help. The AirVPN client does have this network lock feature, that prevents any outside connection if the VPN drops, using some iptables method (again, I don't know how it works exactly), but it should not block any local network connections - my SMB shares, local ssh connections and stuff like that work fine.
I'm using the Minimserver 0.8.3f version with desktop integration, installed according to the instructions.
Any tips? Thanks.