You only need to click once, they all work this way for me, interestingly if I double click-drag the display panel moves for me, but not the minimap or resource bar.
This may be related to the problems John was having with scrollbar buttons never getting mouseUp() events... will have a play on linux later and see if I get the same results as John, if it is a linux thing, it'll likely be causing a few GUI glitches.