jump from VMGM to titleset

This action is refused by dvdauthor 0.7.0 from the vmgm :

jump titleset 1 title 1;

 ERR:  That form of jumping is not allowed
 ERR:  in VMGM pgc 1, button 1


While this one works :

jump title 1;

Is it normal? The manpage didn't light anything in me ;-)

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