Strange: Bison call yacc automatically?

[Jibin Han]

Hi,
    I wonder if you ever see such strange problem. I have a makefile to call
BISON generate C file and then run C compiler to compile the generated C file,
but when I check the make log file, I see a really strange thing: just after
Bison finishes and some file copy I made, yacc is started! it read the parser
file again, and do some tragedy work.
    I checked through my makefile, can not figure out why yacc is started.
    Any idea?

Thanks.