> I'm still curious as to why the "<< { } \\ { } >>" voices interact
> with the tuple bracket to get an unexpected result, but I suppose
> that it doesn't matter.
In your original example, at the third eighth of the triplet, the main
voice has no event (i.e., there is neither a rest nor a skip assigned
to voice `""`), which makes LilyPond close the open beam spanner at the
second eighth of the triplet.
Werner
