Scenario to reproduce the problem:

1. open a graph in "Monitoring" -> "Graphs";
2. use the mouse to select an interval from the past;
3. press F5 and note that the graph shows a different interval, but date and time in the upper right corner of the slider remained the same;
4. press F5 again and note that the graph shows the same interval as in (3), but date and time in the upper right corner of the slider changed to current time.