Hi Massimiliano,
Do use 2.19.82. Although it's modestly termed 'unstable', it is actually very very stable. This use of the term unstable is an open source development convention more than anything in the context of lilypond. The lilypodndreleases are remarkably stable in the last couple of years. Invariably when I post such a comment the development team will jump in say but they are unstable. Yes, but they are also publicly available on the website and practice and experience shows that you are pretty safe using them. I hammer 2.19.82 hard all day and can't break it. It has many advantages over 2.18 especially if you are doing the sort of work I imagine you are. Just my A$2 worth.
Andrew