Intriguing. I see a similar difference:

C:\test>set TEST=abc£
C:\test>echo %TEST%
abc£

perl -MWin32::Console -E"say '1:', $ENV{TEST};say Win32::Console::Outp
+utCP; 
system q[perl -MWin32::Console -E\"say '2:', $ENV{TEST};
     say Win32::Console::OutputCP;\"]"
1:abcú
850
2:abc£
850
[download]

And the difference seems to be internal to Perl somehow.