osgearth_measure not measure correct with multi screen

[caishanli]

When I start osgearth_measure with one screen(Viewer.setUpViewOnSingleScreen) using gdal_tiff.earth, and click on the earth to measure distance, a red line will fllow the mouse, all is ok. But when I use two screen(Viewer.setUpViewAcrossAllScreens), two full window will show the earth, but when I click the left part of earth(left screen), the red line is show in the right part(right screen). And when I click on the right part of earth, the line is show in the left part. And the left top UI shows the distance is missing too. I use osg git master and osgearth git master.