Winbox 4 delayed display with Ros 6.49.18 ?

I am currently configuring a new router RB5009 with Ros 7.18.2. With Winbox 4 every change is displayed immediately. On my RB4011 with Ros 6.49.18, every change is only displayed when I scroll or briefly click on another setting. Is this a “bug” under Ros 6.x ?
br, Richard