Problem: When loaded, one link throttling other

Hi,

I’m testing Mikrotik on my wireless network that worked for years on win 2k3 and i have stumbled to one annoying problem:

when i load one ptp backbone link, other ptp links are throttled.

eg.

3 routers

router1: 1 wlan card + lan (wlan Bridge conn to router2)
router2: 2 wlan cards + lan (1 wlan station conn to r1, 2. bridge conn to router3)
router3: 1 wlan card + lan (wlan station conn to r2)

all wlan cards are working @ 2,4GHz
link router1 - router2 working @ 2+ MB/s
link router2 - router3 working @ 2+ MB/s

problem:

when i have transfer from router1 to router2, connection to router3 is throttled (bandwidth drops to 100kB/s),
also, when i try to transfer something from network behind router3 to router1, speed drops to max 500kB/s

ip addresses as follow:
r1 lan 10.10.1.x
r1 wl 10.10.254.x

r2 wl1 10.10.255.x
r2 wl2 10.10.254.x
r2 lan 10.10.2.x

r3 wl1 10.10.255.x
r3 lan 10.10.3.x

tried with static routes and ospf (have also backup conn r1-r3), the same

on wireless tried with nstream on, and off, also with superG on and off… all the same

hw:
r1: pentium3, 800 mhz, intel mbo i815, 512 ram, AR5212, PQI 64mb disk-on-module
r2: pentium3, 1200 mhz, asus mbo i815, 128 ram, AR5212 x2, PQI 64mb disk-on-module
r3: pentium4, 2400 mhz, dfi mbo i845, 1024 ram, AR5413, PQI 64mb disk-on-module

any suggestions?