[CentOS] Scope of classes in CFE 3.10.2 on CentOS 7

Hi folks,

I have a question concerning scope of classes in CFEngine 3. I run CFE 
3.10.2 on CentOS 7.4.

# cf-agent -V
CFEngine Core 3.10.2

# cat /etc/redhat-release
CentOS Linux release 7.4.1708 (Core)

I'm logged in as root and located in current working dir /root. I have 
the following file

# ll ./samples/scope_of_class.cf
-rwx------. 1 root root 720 10. Jul 16:33 ./samples/scope_of_class.cf

with content

----BEGIN----------------------------------
bundle agent scope_of_class()
{

   vars:
     any::
       "web_servers" slist => {
         "ws-1.example.com",
         "ws-2.example.com",
         "webserver.example.com",
       };

   methods:
     any::
       "scope_of_class_b1" usebundle => scope_of_class_b1( 
$(scope_of_class.web_servers) );

}

bundle agent scope_of_class_b1( server )
{

   classes:
     any::
       "is_dir"
         expression => isdir( "/tmp/scope_of_class/$(server)" ),
         scope => "bundle";

   reports:
     is_dir::
       "is_dir is SET";
     !is_dir::
       "is_dir is UNset";
     any::
       "server = $(server)";

}
----END------------------------------------

 From my understanding the scope "bundle" is default for a class 
definition inside a bundle of type agent, but I added the scope to be 
sure. The definition of class is_dir should depend on directories 
existing inside /tmp/scope_of_class. I have two subdirectories

# ls -1 /tmp/scope_of_class/
webserver.example.com
ws-1.example.com

but when I run CFE I do NOT get expected behaviour for the definition of 
class is_dir:

# cf-agent -IK --file ./samples/scope_of_class.cf --bundlesequence 
scope_of_class
     info: Using command line specified bundlesequence
R: is_dir is SET
R: server = ws-1.example.com
R: is_dir is UNset
R: server = ws-2.example.com
R: server = webserver.example.com

When the bundle scope_of_class_b1 is processed for parameter 
webserver.example.com I expect is_dir to bet set, but from the report it 
seems not to be set.

If I change the slist definition to hold "webserver.example.com" as the 
first entry, then the class is_dir is set correctly:

# grep slist ./samples/scope_of_class.cf -A 4
       "web_servers" slist => {
         "webserver.example.com",
         "ws-1.example.com",
         "ws-2.example.com",
       };
# cf-agent -IK --file ./samples/scope_of_class.cf --bundlesequence 
scope_of_class
     info: Using command line specified bundlesequence
R: is_dir is SET
R: server = webserver.example.com
R: server = ws-1.example.com
R: is_dir is UNset
R: server = ws-2.example.com

It also works "correct" (or as expected by me) if "ws-2.example.com" is 
first entry in the slist definition:

# grep slist ./samples/scope_of_class.cf -A 4
       "web_servers" slist => {
         "ws-2.example.com",
         "ws-1.example.com",
         "webserver.example.com",
       };
# cf-agent -IK --file ./samples/scope_of_class.cf --bundlesequence 
scope_of_class
     info: Using command line specified bundlesequence
R: is_dir is UNset
R: server = ws-2.example.com
R: is_dir is SET
R: server = ws-1.example.com
R: server = webserver.example.com

I do not understand why the ordering inside slist influences how the 
class is_dir will be defined later by CFE for each processing of 
scope_of_class_b1.

Some background information: my aim is to create webserver vhost 
configuration files where I have two variants, one with SSL 
configuration and one without SSL configuration. Which one to configure 
depends if the directory with the SSL certificate exists for a given 
vhost or not. I'll replace the report promise type by a file promise 
type, which should bring the correct vhost configuration file in place, 
assumed that I understand how the scope of the class definition works.

Thanks in advance for any help or explanation of that behaviour.

Regards,

Meikel