'Add related contents that need translation' option works incorrectly

Description

Steps to reproduce

1. Create a project (named Project1).

• Content1 contains Block1.
• Content2 contains Block2; Content1 is dragged and dropped to ContentArea of Content2.
  2. Select Content2 in the Page tree
  3. From the Languages gadget, open its context menu in the English language, and select 'Add to Translation Project'.
  4. Select the corresponding project,
  5. Check 'Add related contents that need translation' option.
  6. Click the Save button.

Expected: Content1, Content2, Block2 should be added to the translation project.
Actual: Content1, Content2 are added to the translation project. Block 2 isn't added to the translation project.

Note: Tested on CMS10 + EPiServer.Labs.LanguageManager version 3.0.4-pre-000035