Conditional Config Ordering

I don't understand some of the ordering dependencies in the  
conditional configuration stuff.  I'm using lighttpd 1.4.19.

For example, this first method doesn't work ("server.error- 
handler-404" is never set):

> $HTTP["url"] =~ "^/foobar/" {
>    $HTTP["useragent"] != "my-ua-str" {
>        server.error-handler-404 = "/foobar/req_error_handler.php"
>    }
> }

while merely swapping the order of the clauses makes it work  
correctly depending on the incoming request:

> $HTTP["useragent"] != "my-ua-str" {
>    $HTTP["url"] =~ "^/foobar/" {
>        server.error-handler-404 = "/foobar/req_error_handler.php"
>    }
> }

There are times when one order is much more convenient than another  
so it would be better if ordering wasn't such an issue (this is just  
one example, I've tripped over similar ordering issues several times).

Is there logic behind this that isn't obvious?

Perry