by H.G.Muller » 04 Aug 2013, 09:14
Indeed, the new default mode is sweep selection, where you vertically move the mouse with the right button pressed until the piece you want appears.
This can be controlled with the (persistent) command-line option -pieceMenu true|false. (Except that the GTK version of XBoard does not support popup menus in general yet, so that setting it to true would make it impossible to put pieces in the position.)