Redmine

Hello,
I've been struggling with this for weeks now and finally can tell what is going wrong, hope you can help me.

I've got a custom list field, named Module, with not default value and with the 'required' option set. Now, I've got this project with a main issue and about 200 hundred sub-issues with even more sub-issues. I use this project as a template, so from time to time, I copy the main issue to other projects with the 'copy subtasks' option set. Target projects also feature the same custom list field, but copying the main issue and subtasks just fail as only the main task is copied. Checking logs, this message pops out:

Could not copy subtask #8475 while copying #8473 to #20765 due to validation errors: Module cannot be blank
Could not copy subtask #8476 while copying #8473 to #20765 due to validation errors: Module cannot be blank

Both # 8475 # 8476 are subtasks of # 8473, the main issue, and I can tell Module has its value fulfilled, so I don't get the point of that warning. Funny thing is, that if I run the same copy BUT without changing the target project, this is, duplicating issues within the same project, it just works!, and Module has its correct value. At that point, I move the issues to the desired target project and I'm done, but this workaround it's slow as I have to do the same operation several times because I can't select more than 100 hundred issues at a time.

This are my settings.

Environment:
  Redmine version                3.2.0.stable
  Ruby version                   2.1.5-p273 (2014-11-13) [i386-mingw32]
  Rails version                  4.2.5
  Environment                    production
  Database adapter               PostgreSQL
SCM:
  Filesystem                     
Redmine plugins:
  no plugin installed

I this a known bug or an expected behavior?, did I miss something?