I don't think the problem is the cyclic references -- I think the problem is a typo between DocumentManager and Mokslas::DocumentManager, as bronto already suggested. Cyclic use statements are no problem for Perl:

file mod1.pm:
  package mod1;
  use mod2;
  sub import {
    print "mod1 imported from " . (caller)[1] . "\n"
  }
  1;

file mod2.pm:
  package mod2;
  use mod1;
  sub import {
    print "mod2 imported from " . (caller)[1] . "\n"
  }
  1;

file use.pl:
  #!/usr/bin/perl
  use lib '.';
  use mod1;
  use mod2;

output:
  $ perl use.pl
  mod2 imported from mod1.pm
  mod1 imported from use.pl
  mod2 imported from use.pl
  $
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require and use will only load the file if it's not already loaded in %INC. Notice how mod2 never imports mod1.

blokhead