INSTALL_BASE weirdness

Hi,

I just subscribed to this list. I'm the maintainer of the Geo::GDAL 
module in CPAN. I just added to its README this:

The Perl bindings use ExtUtils::MakeMaker, which accepts (from version 
6.31) argument INSTALL_BASE to change where the module will be installed.

GNUmakefile in this directory calls

perl Makefile.PL INSTALL_BASE=$(INST_PREFIX)

to honor the overall location where GDAL is to be installed.

It seems that plain "perl Makefile.PL" is different from "perl 
Makefile.PL INSTALL_BASE=/usr/local" in that the former will install 
into /usr/local/lib/perl and the latter will install into 
/usr/local/lib/perl5. It may easily lead to several versions of 
Geo::GDAL in your machine.

So, why the difference? I've been bitten by this many times but only now 
did look into this.

Best,

Ari Jolma