Move a project to subgroup delete all other projects

Summary

You have:

- G1
  \- P1

- G2
  \-SG2
    |- P2
    \- P3

If you "Transfer Project" P1 (Settings -> General -> Advance) to G2/SG2, the projects P2 and P3 disappears.

Steps to reproduce

Create a structure like in the previous section. In project P1 go to Settings -> General -> Advance and Trasnfer Project to subgroup G2/SG2

What is the current bug behavior?

All the projects in the targert subgroup (P2 and P3) disappears.

What is the expected correct behavior?

The content on the target subgroup should not disappear. SG2 should contains P1, P2 and P3.

Output of checks

This bug happens on GitLab.com