discontinuity of `eps-box-padding` at value 0
If you replace in this example
\include "lilypond-book-preamble.ly"
#(ly:set-option 'eps-box-padding 0.00001)
\paper { indent = 0 }
{ c' }
value 0.00001 with 0 (or 0.0, since sometimes LilyPond makes a distinction between integers and floating values), the left padding suddenly disappears.
This discontinuity is neither documented nor useful; I thus believe it is a bug.