And as for why it didn't work, look at this output:

$ cat Spoo.pm
print "pre package: ", __PACKAGE__, "\n";
package Spoo;
print "post package: ", __PACKAGE__, "\n";
1;
$ perl -MSpoo -e 0
pre package: main
post package: Spoo
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In your code your use Data::Dumper line (which is implicitly running Data::Dumper->import()) is being executed in the main package. When you subsequently try and use Dumper() Perl sees an unqualified sub name (since it didn't get imported into Misc::Test) and gripes.