How to reproduce:
1. Open the attached "Test1073476.zip" project
2. Select GameObject Prefab from the Prefabs folder
3. In the Inspector window press Open Prefab
4. Add TestSpriteMesh from the Sprites folder as a child of the Prefab
5. Press Ctrl + S or have Auto Save turned on
6. Observe the mouse cursor indicating the saving process

Expected result: Editor saves project once
Actual result: Editor gets stuck in an infinite saving process loop

Reproducible with: 2018.2.0x-ImprovedPrefabs, 2018.3.0a10

Notes:
1. Entering Play mode stops the loop
2. Any further change to the prefab will trigger the loop again if the project is saved

Update: Fixed in Anima2D 1.1.6b1 version