Reproduction steps:
1. Open the attached project;
2. Open the scene "Sandbox";
3. Click on the object "Cube";
4. Drag the script (for example "Item.cs") over the object component "TestScript.cs" till the Unity crashes;

Actual result: Unity crashes at <TypeTreeIterator::Next>.
Expected result: Unity should not crash.

Note: Unity does not crash, if the "EditorGUILayout.ObjectField(Item);" (line 34) in the EditorTest.cs is commented.

Reproduced with: 5.5.0a6, 5.5.2p3, 5.6.0f1, 2017.1.0a3

Can not be tested with 5.4 version, because the error shows (error.jpg) and when the error line is commented, Unity does not crash.