message: Small fix for mouse up in the Splitter.
diff: @@ -213,6 +213,10 @@ export class Splitter extends ThemeableElementBase {
  }
  private _handleMouseUp(ev: MouseEvent): void {
  + if (this._dividerDrag === NOT_DRAGGING) {
  + return;
  + }
  +
  const target = <HTMLElement> ev.target;
  this._log.debug("target: ", target);
  this._log.debug("has divider: ", target.classList.contains(CLASS_DIVIDER));
  