If you set spacer to whole width (don't know engl. labeling), the last button/menu right from the spacer will not shown (see attachment). This is reproducable with every toolbar.
Seems to be new, worked before (changed to 184.108.40.206, but don't know if it's also in 220.127.116.11).
Is it the visual style that you're using which means there's more space than usual between each menu item, or is it something else like lots of space characters around the labels? I wonder if whatever it is is confusing Opus.
It' the visual style (spacer). You can set its size manually or use max. width, which automatically sizes. It worked before. Tried this on 2 different pc.