configure created with buildconf does not show unknown options

So I'm installing PHP 5.2.10.  I run configure with the same options I
had for 5.0.  At the end it complains about some unknown options.
I'll just use two examples "--enable-yp"  and
"--with-pdflib=/usr/local/share/pdflib/bind/c'

Now I downloaded and extrated pdf from pecl and put it in ext/pdf.  I
didn't do anything about yp tho.

Next I removed configure and ran "buildconf --force"

Then I ran the new configure with the exact same options as before.

As expected it didn't complain about
"--with-pdflib=/usr/local/share/pdflib/bind/c' however since I did
nothing about yp, I shouldn't I have gotten another error message
about "--enable-yp" being an unknown option?

There were also a number of other options that should have been
unknown I've omitted them in the interest of brevity.

Is there something I can do with buildconf that will make the new
configure tell me about unknown options?

Thanks in advance.