Reproduction steps:
1. Open the attached project "RewiredU2018_1.zip";
2. Go to Window -> Rewired -> Extras -> Control Mapper and select Install;
3. Open the Assets/Rewired/Extras/ControlMapper/Examples/ControlMapperDemo scene;
4. Click the ControlMapper object in the hierarchy;
5 Scroll down to the bottom and open the foldout Internal Data - > Prefabs.

Expected results: all prefabs have their object references.
Actual results: All object references are lost.

Note: If you reinstall Color Mapper again (from the same menu), all prefab have their references now. This issue happens only when installing this asset for the first time.

Reproduced only on 2018.2.0x-ImprovedPrefabs_ff19e2e229d2 version.