I have installed Xboard from HGM git repository, date stamp 2010-04-01 (but about tells me it is 2010-03-27). This version has one-click moving, but in general I do stupid stuff whith this so I set it to false. The one-click move has two behaviours as described in HGM's web site: one-click will perform a move if there is only one legal move from / to the square clicked, and double-clicking a piece will perform a capture, if that pice has only one capture. As far as I can tell, the first one-click move indeed is disabled (e.g. clicking on e4 in the initial position should move e-e4, but it does not), but the second "one-click" (double-click as capture) does work - and it caused me to do many catastrophic captures on FICS. I checked /usr/local/etc/xboard.conf, there is no oneClickMove there, and .xboardrc has oneClickMove set to false.
As I understand from HGM web site, this is not the intended behaviour.
In addition, I also have premove on, and if I double-click a piece, to select and then unselect the piece (say, I see it is a bad move, or find a better move), and then try to select a new piece but my opponent moves before I am able to, the double-click intended as select-unselect will have the effect of the double-click capture. I think this is a bit of incovenient behaviour for people that will use both premove and smart-clicks - I don intend to, but anyway, I think these options will cause this kind of "blunders" if they stand as they are.