gzclient makes simulation real time factor increase; How is this possible?

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Hello, I have a bit of a mysterious puzzle. If I run gzserver then gz stats I get an expected real time factor of 1.00. If I then gz physics -u 0, I get a real time factor on an empty world of 215. This stays relatively stable for several minutes. If I then run gzclient the real time factor increases to 230. If I close gzclient it remains stable at 230 for at least several minutes and possibly indefinitely. This is reliable and repeatable on my install.

Running the turtlebot ROS+Gazebo sim in the willow garage environment yields a real time factor of 30. Running gzclient yields a real time factor of 40. Closing gzclient yields a stable real time factor of 50. I have no idea what is going on here.

Two questions:

1. Is this plausible, or some kind of artefact of how RTF is computed?
2. Is RTF a reliable performance measure, or should I be using something else?