Make sure, that we're not starting a second selection.

lib/codemirror.js

@@ -87,6 +87,7 @@
       focused: false,
       suppressEdits: false, // used to disable editing during key handlers when in readOnly mode
       pasteIncoming: false, cutIncoming: false, // help recognize paste/cut edits in input.poll
+      selectingText: false,
       draggingText: false,
       highlight: new Delayed(), // stores highlight worker timeout
       keySeq: null,  // Unfinished key sequence
@@ -3540,7 +3541,10 @@
 
     switch (e_button(e)) {
     case 1:
-      if (start)
+      // #3261: make sure, that we're not starting a second selection
+      if (cm.state.selectingText)
+        cm.state.selectingText(e);
+      else if (start)
         leftButtonDown(cm, e, start);
       else if (e_target(e) == display.scroller)
         e_preventDefault(e);
@@ -3738,6 +3742,7 @@
     }
 
     function done(e) {
+      cm.state.selectingText = false;
       counter = Infinity;
       e_preventDefault(e);
       display.input.focus();
@@ -3751,6 +3756,7 @@
       else extend(e);
     });
     var up = operation(cm, done);
+    cm.state.selectingText = up;
     on(document, "mousemove", move);
     on(document, "mouseup", up);
   }