Having two files:

$ cat M.pm 
print join(',', M->plugins), "\n";

package M;
use Module::Pluggable search_path => [ 'M' ];

$ cat M/X.pm 
package M::X;
1;

`perl M.pm' should locate M::X plug-in and print the name to standard output like this:

$ perl -I/home/petr/Module-Pluggable/lib M.pm 
M::X

However it does not.

This issue has been reported to upstream <https://rt.cpan.org/Public/Bug/Display.html?id=89680> and fixed in commit:

commit 7872bc27ac7f828a6b53d00717abdf83f2d1866d
Author: Simon Wistow <simon>
Date:   Tue Oct 22 09:32:27 2013 -0700

    Allow single letter package names

All Fedoras with perl-Module-Pluggable < 5.00 are affected.