Redmine

It's a generic "this is an invalid parent ID" changing it to "" then "1000" works fine though.

+1
We have same issue.
Working around by once detaching the child as an independent one.

Using Redmine v2.5.1.

In app/models/issue.rb, there is the following bit of code.

      elsif (@parent_issue != parent) && (all_dependent_issues.include?(@parent_issue) || @parent_issue.all_dependent_issues.include?(self))¬
        #go2null:errors.add :parent_issue_id, :invalid¬
        errors.add :parent_issue_id, " - bad depends"¬
      elsif !new_record?¬
        # moving an existing issue¬
        if @parent_issue.root_id != root_id¬
          # we can always move to another tree¬
        elsif move_possible?(@parent_issue)¬
          # move accepted inside tree¬
        else¬
          errors.add :parent_issue_id, :invalid¬
        end¬
      end¬

It appears that the move accepted inside tree will never be invoked because (all_dependent_issues.include?(@parent_issue) || parent_issue.all_dependent_issues.include?(self)) will always be true.

In fact, both all_dependent_issues.include?(@parent_issue) and parent_issue.all_dependent_issues.include?(self) will always be true when moving a grandchild to a grandparent, or vice versa.

Or am I reading this wrong?

The elsif was added in r11641 to fix #8794 Circular loop when using relations and subtasks.

Based on this, it seems that #13654 (Can't set parent issue when issue relations among child issues are present) may also be related.

It seems that the previous code (r3573), before r11641, which implemented subtasking (#443), allowed moving grandchild (descendents) around the tree. (# move accepted inside tree).