perl -d:Trace -e " eval q{  use open qw/ :std :encoding(utf8) /; use T
+est::Exception; }; warn $@ "   2>2


perl -MCarp::Always -e "  use open qw/ :std :encoding(UTF-8) /; use Te
+st::Exception; "


perl -e "  use open qw/ :std :encoding(UTF-8) /; use Test::Exception; 
+"
[download]

Encode                 2.47
Encode::Alias          2.16
Encode::Config         2.05
Encode::Encoding       2.05
Exporter               5.66
Exporter::Heavy        5.66
PerlIO                 1.07
PerlIO::encoding       0.14
Sub::Uplevel           0.24
Test::Builder          0.98
Test::Exception        0.31
XSLoader               0.15
base                   2.18
bytes                  1.04
constant               1.21
open                   1.08
vars                   1.02
warnings               1.12
warnings::register     1.02
[download]

5.12.2 has

Encode                 2.43
Encode::Alias          2.14
Encode::Config         2.05
Encode::Encoding       2.05
Exporter             5.64_01
Exporter::Heavy      5.64_01
PerlIO                 1.06
PerlIO::encoding       0.12
Sub::Uplevel           0.22
Test::Builder          0.98
Test::Exception        0.31
XSLoader               0.15
base                   2.15
bytes                  1.04
open                   1.07
vars                   1.01
warnings               1.09
warnings::register     1.01
[download]

Definitely an perl/perlio/open/Encode bug ... here is why I think that

$ set PERL_ENCODE_DEBUG=999

$ perl -e " use Devel::Modlist; use open qw/ :std :encoding(utf8) /; u
+se Test::Exception;  "
Encode::utf8 XS on at C:/perl/5.14.1/lib/MSWin32-x86-multi-thread/Enco
+de.pm line 298.
Bareword "xception" not allowed while "strict subs" in use at C:/perl/
+site/5.14.1/lib/Test/Exception.pm line 4.
Compilation failed in require at -e line 1.
BEGIN failed--compilation aborted at -e line 1.

$ perl -e " use Devel::Modlist; use open qw/ :std :encoding(UTF-8) /; 
+use Test::Exception;  "
Encode::utf8 XS on at C:/perl/5.14.1/lib/MSWin32-x86-multi-thread/Enco
+de.pm line 298.
eval "utf-8-strict" at C:/perl/5.14.1/lib/MSWin32-x86-multi-thread/Enc
+ode/Alias.pm line 32.
(?^i:\bUTF-8$), utf-8-strict at C:/perl/5.14.1/lib/MSWin32-x86-multi-t
+hread/Encode/Alias.pm line 45.
find_alias(Encode, UTF-8)->name = utf-8-strict at C:/perl/5.14.1/lib/M
+SWin32-x86-multi-thread/Encode/Alias.pm line 75.
find_alias(Encode, UTF-8)->name = utf-8-strict at C:/perl/5.14.1/lib/M
+SWin32-x86-multi-thread/Encode/Alias.pm line 75.

$ perl -e " use Devel::Modlist; use Test::Exception;  use open qw/ :st
+d :encoding(UTF-8) /; "
Encode::utf8 XS on at C:/perl/5.14.1/lib/MSWin32-x86-multi-thread/Enco
+de.pm line 298.
eval "utf-8-strict" at C:/perl/5.14.1/lib/MSWin32-x86-multi-thread/Enc
+ode/Alias.pm line 32.
(?^i:\bUTF-8$), utf-8-strict at C:/perl/5.14.1/lib/MSWin32-x86-multi-t
+hread/Encode/Alias.pm line 45.
find_alias(Encode, UTF-8)->name = utf-8-strict at C:/perl/5.14.1/lib/M
+SWin32-x86-multi-thread/Encode/Alias.pm line 75.
find_alias(Encode, UTF-8)->name = utf-8-strict at C:/perl/5.14.1/lib/M
+SWin32-x86-multi-thread/Encode/Alias.pm line 75.

$ perl -e " use Devel::Modlist; use Test::Exception;  use open qw/ :st
+d :encoding(utf8) /; "
Encode::utf8 XS on at C:/perl/5.14.1/lib/MSWin32-x86-multi-thread/Enco
+de.pm line 298.
Config
Encode                 2.47
Encode::Alias          2.16
Encode::Config         2.05
Encode::Encoding       2.05
Exporter               5.66
Exporter::Heavy        5.66
PerlIO                 1.07
PerlIO::encoding       0.14
Sub::Uplevel           0.24
Test::Builder          0.98
Test::Exception        0.31
XSLoader               0.15
base                   2.18
bytes                  1.04
constant               1.21
open                   1.08
vars                   1.02
warnings               1.12
warnings::register     1.02
[download]

Basically a serious bug is in there in XS land somewhere, will see what happens after upgrades

Eeeew

perl5160delta use and require are no longer affected by the I/O layers active in the caller's scope (enabled by open.pm) [perl #96008].

Bug #96008 for perl5: use and require are affected by the open pragma

Thank you for digging into this. I also learned that 5.14.3 is not officially supported, so I am inclined not to worry about the bug and the test failure.

I would like to have zero test failures, however, so I am thinking I will change the use open() call to a use if ... statement so it doesn't load under the broken perl/OS combo.

The way forward always starts with a minimal test.