Can IsFallback be used with Weighted Algorithm ?

[yashkhare]

I have 3 target servers say - t1, t2 and t3 . Below is a simple loadbalancer config for the same :

<LoadBalancer>
<Algorithm>Weighted</Algorithm>
<Server name="t1">
<Weight>1</Weight>
</Server>
<Server name="t2">
<Weight>1</Weight>
</Server>
<Server name="t3">
<IsFallback>true</IsFallback>
</Server>
<ServerUnhealthyResponse>
<ResponseCode>204</ResponseCode>
<ResponseCode>400</ResponseCode>
<ResponseCode>500</ResponseCode>
<ResponseCode>502</ResponseCode>
<ResponseCode>503</ResponseCode>
</ServerUnhealthyResponse>
</LoadBalancer>

With the above config, whenever there is a failure at t1  with the above mentioned response codes it invokes t2. Ideally it should invoke t3 in such cases. Any idea why is it happening like this ?