Hi Paolo,
> it's of course _erroneous_ output, because it leads to what in common programming is called UB:
It’s perfectly defined behaviour:
http://lilypond.org/doc/v2.18/Documentation/internals/fingering
font-encoding (symbol):
'fetaText
The font encoding is the broadest category for selecting a font. Currently, only lilypond’s system fonts (Emmentaler) are using this property. Available values are fetaMusic (Emmentaler), fetaBraces, fetaText (Emmentaler).
This is not a defined *behaviour*. This is a defined _default_.
The UB is the result of the compiler, which behaves in two different ways if you change the backend without changing the input, due to the inapplicability of Feta font for normal text.
It's like if you access the 11th element of an array of size 10 (defined default). It can crash or it can give weird results (---> undefined behavior)
Cheers,
P