problem with &expire_func

hi there

i found another problem with bro.
this time it is the expire_func which makes trouble.
when i have a policy file like this:

global mytable: table[addr] of bool &write_expire=10sec &expire_func=myfunc;

function myfunc(t: table[addr] of bool , idx: any): interval {
    local srcIP: addr;

> print network_time(),"help!!!";

    [srcIP] = idx;

    return 0secs;

it ends in an error like this:

1108032092.49407, help!!!
1108032092.494068 <no location> ( bad tag in Val::CONVERTER

i tested several constellations and noticed, that it is impossible to use idx when a table has only one index.

any help welcome.