An odd problem occur when I am studying gnu make

Hi, I happen to find an odd problem when I am experiment with gnu
make. And I have written a really simple makefile to test how make
work when chaining rules together to generate the   target.
My makefile is somewhat look like this:

#makefile
pro: ok.h pro.c

%:%.c

%.c:
	@echo generate $@

%.h:
	@echo generate $@

%.l:
	@echo use %.l rule and generate $@

#%:%.o
#	@echo $+

%:%.l pro.c
	@echo use .l rule and generate $@

There is only a makefile in the folder. That means every file
indicated in this makefile are not really exist. I just what to test
how make work.
But when I run make in my bash shell's command line, make output an
odd result(I found it odd at least). The make program output:

generate pro.c
use %.l rule and generate makefile.l
use .l rule and generate makefile
generate ok.h
use %.l rule and generate pro.l
use .l rule and generate pro

I haven't specified anything that relate to the file makefile, by why
does make have to generate makefile.l and makefile? Is that an bug or
else?

Thank you very much.