### Sagetex : hyphen in filename forbidden ?

I want to cross-compile (pdflatex + sage + pdflatex) a TeX file : it's ok with the filename "a-b.tex", but not for a-n.tex, where i get the error message

CRITICAL:root:unknown notebook: None
Error, notebook must be one of default, ipython, sagenb but got None

It seems that the problem is with the "-n" part of a-n.tex

it's a bug or a feature ?
lg

macosX 10.10.1 + sage 6.4.1