make clean has error

OS: Mac OS X 10.9, Version: github master

step1: make
step2: make clean # remove src/sregex/sre_yyparser.[ch] files
step3: make

output:
BISON     src/sregex/sre_yyparser.h
src/sregex/sre_yyparser.y:60.10-36: syntax error, unexpected string, expecting =
make: *** [src/sregex/sre_yyparser.h] Error 1