VPLS link fails under load while underlying network does not

Hello, I have the following problem.

When i stress a VPLS link with traffic, it fails for a few seconds while none of the underlying wireless and wired links fail.
You can see this from the attached screenshots, while i was running two bandwidth tests at the same time, one over the VPLS link and one over MPLS.
I believe this started when i inserted the RB711GA-5HnD into my network.

my network was created according to this example http://wiki.mikrotik.com/wiki/Manual:MPLSVPLS

ROS is 5.7 for the atoms and 5.8 for the RB711

[admin@costas] > mpls forwarding-table print                            
Flags: L - ldp, V - vpls, T - traffic-eng 
 #   IN-LABEL      OUT-LABELS  DESTINATION                    I NEXTHOP 
 0   expl-null    
 1 L 1457          16          192.168.255.3/32               c 192.168.
 2 L 1459                      192.168.255.2/32               c 192.168.
 3 L 1460                      192.168.4.0/24                 c 192.168.
 4 L 1461          21          192.168.255.4/32               c 192.168.
 5 L 1462          20          192.168.3.0/24                 c 192.168.
 6 V 1463                      costas-spigias                
[admin@costas] > mpls remote-bindings print                             
Flags: X - disabled, A - active, D - dynamic 
 #    DST-ADDRESS        NEXTHOP         LABEL       PEER               
 0  D 192.168.255.3/32                   16          192.168.255.4:0    
 1  D 192.168.3.0/24                     impl-null   192.168.255.4:0    
 2  D 192.168.1.0/24                     impl-null   192.168.255.4:0    
 3  D 192.168.255.4/32                   impl-null   192.168.255.4:0    
 4  D 192.168.255.2/32                   19          192.168.255.4:0    
 5  D 192.168.4.0/24                     20          192.168.255.4:0    
 6  D 192.168.2.0/24                     17          192.168.255.4:0    
 7  D 192.168.255.1/32                   18          192.168.255.4:0    
 8 AD 192.168.255.3/32   192.168.2.2     16          192.168.255.2:0    
 9  D 192.168.1.0/24                     18          192.168.255.2:0    
10 AD 192.168.3.0/24     192.168.2.2     20          192.168.255.2:0    
11  D 192.168.2.0/24                     impl-null   192.168.255.2:0    
12 AD 192.168.255.4/32   192.168.2.2     21          192.168.255.2:0    
13  D 192.168.255.1/32                   19          192.168.255.2:0    
14 AD 192.168.255.2/32   192.168.2.2     impl-null   192.168.255.2:0    
15 AD 192.168.4.0/24     192.168.2.2     impl-null   192.168.255.2:0

MTU everywhere is at default (1500 for the wireless and wired interfaces and mpls-mtu is 1508)

I can provide with supout.rip files and whatever else is needed to help solve this problem
mynetwork.png
bwtest 2.PNG
bw test.PNG