When the author name with "-", biber tends to generate dummy characters around the name. For example, one input in bib file as the following.
@article{Baker,
author = {Baker, F.B. and Al‐Karni, A},
journal = {Journal of Educational Measurement},
pages = {147--162},
title = {{A comparison of two procedures for computing IRT equating coefficients}},
url = {http://onlinelibrary.wiley.com/doi/10.1111/j.1745-3984.1991.tb00350.x/abstract},
volume = {28},
year = {1991}
}
when the above input compiled in latex, error message will be generated and if check back to the bbl file, the "-" became fffd...
\name{labelname}{2}{}{%
{{uniquename=0,hash=4d61c716006737e01dad3e296d8cb4b2}{Baker}
{B\bibinitperiod}{F.B.}{F\bibinitperiod}{}{}{}{}}%
{{uniquename=0,hash=bbeb8c73c9f3f7bd033ecb2e8bbdab2d}
{Al\x{fffd}\x{fffd}\x{fffd}Karni}{A\bibinitperiod}{A}{A\bibinitperiod}{}{}{}{}}%
}
and the output of pdflatex will be
Baker, F. & AlfffdfffdfffdKarni, A. (1991). A comparison of two procedures for computing IRT equating coefficients. Journal of Educational Measurement, 28, 147–162.
rather than the original one as
Baker, F. & Al-Karni, A. (1991). A comparison of two procedures for computing IRT equating coefficients. Journal of Educational Measurement, 28, 147–162.
Is it a bug of biber or biblatex? And how to fix it?

-. The dash in your file might be some weird unicode character that looks like a dash but isn't the normal one. (In fact, if you copy the character inAl‐Karnifrom your MWE and search for it on this page, you will only find that occurrence of the character; all the other dashes are different characters.) – moewe Apr 01 '14 at 11:53