The values are saved "as is". What goes into the database is what you typed, I don't mess with peoples' data. Er, very much - there _are_ ways in which what you get back is not exactly what you put in. The most noticeable is that the header fields are sorted in order of their keys (if there are several values for the same header key, their order will be preserved, of course). I have also taken it upon myself to not accept comments after values in header fields (for the reason that it messes up the listboxes). Any such header lines will have the comments stripped in the header, and reappear in their full form at the top of the tune body so that you can at least be aware that this has been done, and not lose the comment. In no cases will anything be removed silently from your input.
The question of backup becomes increasingly important. If you type tunes up here, how safe are they, are you likely to lose your work ? This is an important question, and I haven't had to time yet to give it the thought that it needs. For now, use the "Download ABC" facility to keep a copy of what you've done, just in case.