High BackendReuse Rate Problem

[Lusurf Lui]

Hi,

I'm using the Varnish-Cache-3.0.2 and have been encountered a very
strange problem.

I use a random director which is defined like this:
----------------------------------------------------
director randomlb random {
    {
        .backend = app1019;
        .weight = 15;
    }
    {
        .backend = app1018;
        .weight = 15;
    }
    {
        .backend = app1020;
        .weight = 15;
    }
    {
        .backend = app1021;
        .weight = 15;
    }
}
----------------------------------------------------
The problem is that the BackendReuse rate of app1018 is significantly
higher than the other backends.
And this is a simple test case.
----------------------------------------------------
    526 BackendReuse app1018
    ###
    988 BackendReuse app1019
    ###
    561 BackendReuse app1020
    573 BackendReuse app1021
----------------------------------------------------

What should i do to gain a balanced backendreuse rate for all the backends?

Thanks.

---
Lusurf