After verification and a lot of tests, the problem came not from Lyx but from the package used. According to the bibtopic help file, this package "doesn’t work with the ‘unsorted’ citation styles such as unsrt or unsrtdin.9 Use the package multibib.sty instead (see also section 8)."
So... Let's try multibib XD
BibTeX, biblatex and biber ⇒ Multiple Bibliography
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