Children pages aren't added fully to translation projects

Description

Steps to reproduce

1. Create PageA.
2. Create 2 children for PageA, named PageA1 and PageA2.
3. Add PageA to Project1 again with option 'Add all children' is checked.

Expected: PageA, A1 and A2 should be added to Project1.
Actual: PageA, PageA1 are added to Project1; PageA2 isn't added to Project1.

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