Menu disappearing on 3rd Level

Hello,

i am not sure if this is intended, but if i open my 3rd level menu entries, the entire 2nd level menu disappears.
On the sample page it shows the same behavior (click on Test Story 5 here http://menu_block_split.demo.garrigos.cat/node/5 and the 2nd menu level disappears), but i would like to keep my menu visible. How can this be fixed?
Thanks in advance

squishy