issue 720 and 2968: vertical crop when using EPS backend and some kinds of Staff

[Federico Bruni]

Hi folks

Every now and then I come back to this issue.
The last time¹ (two years ago) I was deviated to an interesting 
different workflow. This time I'd be curious to find some pointers for 
a workaround or, better, solutions from developers :-)
The reason why this bug is so annoying is that it prevents me from 
using great tools such as LyLuaTex.

As I wrote today in this comment:
https://sourceforge.net/p/testlilyissues/issues/2968/#c018/5264/1878

a minimal example to reproduce the bug is this:

\version "2.19.82"
\include "lilypond-book-preamble.ly"

\new StaffGroup <<
 \new Staff {
   \repeat unfold 6 a'1*4 \break
 }
 \new TabStaff {
   \repeat unfold 6 g1*4 \break
 }
>>

The second staff at the bottom will be cropped.
This seems to happen (at least with above file) only with TabStaff, 
DrumStaff, RhythmicStaff and VaticanaStaff, while other kinds of Staff 
works fine. Is this a good clue to investigate?

Thanks
Federico

¹ 
https://lists.gnu.org/archive/html/lilypond-user/2016-08/msg00020.html