Steps to reproduce:

1. Open Unity;
2. Create new project;
3. Import "Free_SpeedTrees" package from A$;
4. Add Terrain gameobject (GameObject -> 3D Object -> Terrain);
6. Go to 'Place Trees' tab of the Inspector;
7. Click Edit Trees... -> Add tree;
8. Add 4 or more tree prefabs to the Inspector;
9. Resize Inspector tab;
10. Observe tree preview icons.

Actual result:
At some point tree icons become smaller than initial size. After further resizing icons get bigger again (see attached ActualResizingTreeInspector.gif video).

Regression introduced in 5.4.

Expected result:
Tree icons should preserve the same size when resizing. See attached ExpectedResizingTreeInspector.gif video.

Notes:
- Reproduces on both OSX 10.11.3 and Windows 10;
- Reproduces on 5.4.0b5, 5.4.0b4;
- Doesn't repro in 5.3.2f1;
- Reproes only when having 4 or more trees added to 'Place Trees' tab;
- Also reproes in Paint Texture tab and Paint Details tabs of Terrain component.