Top-scope Puppet function behavior is inconsistent with documentation

Per https://docs.puppet.com/puppet/4.10/lang_write_functions_in_puppet.html it is possible to write Puppet-language functions in the main manifest (top-scope). The warning in the documentation indicates that the behavior, as with other top-scope items, would be to have the function accessible to all modules.

However, if you define a function in the main manifest and then try to call it from a module you will receive an error such as: "Error: Evaluation Error: Unknown function: 'testfunc'". It works fine when called from the main manifest. Calling it with the leading "::" indicating top-scope has no change in behavior.

The expected behavior is that top-scope Puppet language functions would work per the documentation and similarly to their Ruby counterparts.