How to repeat: Go to Monitor->Graphs page for any resource. Click one of the green/red xmas tree lights at the top of the graph section. It should highlight the time slice and pop up a small date/time box at the bottom to indicate what time slice you selected. Now roll the mouse over the gray xmas lights at the bottom of the graphs section. Notice the time popup changes to whatever slice you're rolling over. This should not happen, it should stay fixed on what you've already click-selected. In other words the click selection should disable any rollover popup. If you deselect (which currently isn't possible), then enable the rollover popup again.
i saw this too, and i meant to get back to it. i've been trying to slowly but surely improve the usability of the graphs stuff, so this falls under that umbrella too.
rev3232 - better handling of overlay element with top (availability) and bottom timeline bars; better handling of overlay expanding/collapsing event details, as well as changing the selected events timeslice;
Now it's all rollover (highlight and popup). works for me. rev3416
This bug was previously known as http://jira.rhq-project.org/browse/RHQ-1472