Annotation moved to another panel after adding "metric group"


I am new to grafana. I am using version 6.7.2 (with graphite + statsd).

Here is my scenario:
I have 3 stations collecting metrics station03, station04, station05. I’ve created a variable $station to allow me to select them in the dashboard. The panel is parameterized using the variable $station, so that they are displayed dynamically once I choose the stations I want to see. Recently I added one annotation to station03.

Now, today I’ve added a new station - station02. What surprised me is that, the annotation which was once created in the station03 panel is now shown in the station02 panel.

Am I doing something wrong here ? Seen the annotations in another panel is completely misleading.

many thanks,