For me, this is happening whenever I try to right-click documents selected using shift. The instant I right-click, bam, only one document selected. Hopefully this can be fixed soon. Thanks for the tip about control-selecting, though. That still works.

So the default behavior of the screen split button on the editor is to toggle between horizontal split and no split, with vertical split being the option when you press alt. But when I alt-tab to another window, when I come back, that button (without pressing anything else) now toggles between horiz...