L2TP issue with RDP

Hi people,
I need some help about an issue I’m facing. I have an RB1100AHx2, which we are using for internet access, an IPsec tunnel to a datacenter and L2TP server for people working from home.
The issue is really strange and I can’t find why it’s happening. When I connect from home I can RDP machine in both networks - the local net and the one that we access through the tunnel, that’s how we want it to be. BUT while the RDP to machines in the tunnel connected network is fine, the RDP to machines in the local network suffers regular disconnects which basically makes it unusable.
I ran simultaneous pings to several machines and I noticed lost packets only to the machine that I RDPed to, all other pings were fine. RDP from within the network to those machines works fine, which means that this is some kind of network issue.
Any help and suggestions will be appreciated!

I have similar problems (http://forum.mikrotik.com/t/ipsec-unstable/104482/1). Do you have any ideas for this problem?