I suspect that one platform considers it to be whitespace while the other does not. There is quite a maze of twisty little C macros involved, but isSPACE() is used in the Perl source code to skip leading spaces on strings being interpretted as numbers.

I could certainly see Win32's isspace() (C macro/function) knowing that "\xA0" is whitespace but Unix's not realizing this.

Then there is the twisty maze to consider. When Perl is built, if it appears that locales are supported, then different code might get used for isSPACE().

I certainly don't consider it a bug either way. I find it reasonable to treat "\xA0" as whitespace (a more modern approach) and reasonable to not treat it as such (a more traditional approach). That different builds of Perl might disagree on this point does not surprise me.

                - tye