Fix #586

core/flyout_button.js

@@ -162,6 +162,8 @@ Blockly.FlyoutButton.prototype.onMouseUp = function(e) {
   e.preventDefault();
   // Don't propagate mousewheel event (zooming).
   e.stopPropagation();
-
+  // Stop binding to mouseup and mousemove events--flyout mouseup would normally
+  // do this, but we're skipping that.
+  Blockly.Flyout.terminateDrag_();
   Blockly.Variables.createVariable(this.targetWorkspace_);
 };