What I mean is: is there a way to actually solve the problem ?

Yes, like I said, the solution is force :)

Why? Its pod, an author test, as an end user, you're not even suposed to run it, it makes no sense to keep testing pod for valid syntax

If that doesn't work for you, drop in to the directory, and run podchecker on the various .pm/.pod files until you find the syntax error, then fix it

Or see https://rt.cpan.org/Public/Dist/Display.html?Name=Win32-GUI, some have submitted patches for these typos

way to "hide" a perl secondary window ?

simplest is to use wperl.exe

Or Win32::Process::Create or Win32::API solution