For info: I am on a mac using the latest Safari & Firefox.
In Reporting -> Network Security -> IPS & IMP2P.
When you select Top Rules, then click on the column "Rule" to sort it, the content disappears.
Same thing for Top Groups, on selection of "Group" column.
A weird one:
Always in Reporting -> Network Security -> IPS & IMP2P.
In Safari (4.02 Mac) the default combo is set to "Top Rules"
the same screen in Firefox (3.5 Mac) it defaults to "Top Source Hosts"