subsequent nodes in a namespace in yaml don't get parameters applied

Bug report

Required Info:

• Operating System:
  • Ubuntu 22.04
• Installation type:
  • binaries
• Version or commit hash:
  • humble
• DDS implementation:
  • CycloneDDS
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

Try a params yaml like this:

namespace:
  node1:
    ros__parameters:
      param: 1.0
  node2:
    ros__parameters:
      param: 2.0

Expected behavior

node1 to have param with a value of 1.0, and node2 to have param with a value of 2.0

Actual behavior

node1 has a param set to 1.0 and node2 has a value of param that is the default. The value from yaml is not applied.

Additional information

Also reported here: https://answers.ros.org/question/394231/ros2-how-to-get-multiple-nodes-under-same-namespace-in-yaml-config-file/

Interestingly, having top level duplicate keys works, even though that is not technically valid yaml, like this:

namespace:
  node1:
    ros__parameters:
      param: 1.0
namespace:
  node2:
    ros__parameters:
      param: 2.0

Reproduce the issue in rclcpp with the provided YAML and verify that node1 receives 1.0 while node2 retains its default. Trace the parameter YAML handling and add regression coverage showing that both nodes receive their respective values; done means the second node's parameter is applied correctly.