message: reset tracking point on mouse event
diff: @@ -230,6 +230,7 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  if (!this._state) {
  return;
  }
  + this._onMouseEvent();
  const x = event.localX;
  const y = event.localY;
  @@ -238,6 +239,7 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  }
  public mouseDownEvent(event: MouseEventHandlerMouseEvent): void {
  + this._onMouseEvent();
  this._mouseTouchDownEvent();
  this._setCrosshairPosition(event.localX, event.localY);
  }
  @@ -246,6 +248,7 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  if (!this._state) {
  return;
  }
  + this._onMouseEvent();
  const x = event.localX;
  const y = event.localY;
  @@ -259,6 +262,7 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  if (this._state === null) {
  return;
  }
  + this._onMouseEvent();
  const x = event.localX;
  const y = event.localY;
  @@ -270,7 +274,7 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  }
  public pressedMouseMoveEvent(event: MouseEventHandlerMouseEvent): void {
  - this._startTrackPoint = null;
  + this._onMouseEvent();
  this._pressedMouseTouchMoveEvent(event);
  }
  @@ -278,6 +282,7 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  if (this._state === null) {
  return;
  }
  + this._onMouseEvent();
  this._longTap = false;
  @@ -297,6 +302,7 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  if (this._state === null) {
  return;
  }
  + this._onMouseEvent();
  this._state.model().setHoveredSource(null);
  this._clearCrosshairPosition();
  @@ -710,6 +716,10 @@ export class PaneWidget implements IDestroyable, MouseEventHandlers {
  requestAnimationFrame(animationFn);
  }
  + private _onMouseEvent(): void {
  + this._startTrackPoint = null;
  + }
  +
  private _mouseTouchDownEvent(): void {
  if (!this._state) {
  return;
  