missing ROS_ERR and ROS_FATAL from node log file

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I expected messages from ROS_ERR and ROS_FATAL to end up in the log files together with messages from ROS_INFO etc. But with this code in a node:

ROS_ERROR("Test error");
ROS_WARN("Test warn");
ROS_FATAL("Test fatal");

I find that my log file for the node only contains:

Test warn

The error/fatal messages are printed to the console, and can be found in the rosout.log. I miss them in the node log file and expected them there according to roscpp/Overview/Logging

Am I expecting something wrong?

Using ROS kinetic.