I've been noticing exceptions being thrown in the Editor in a few places. I managed to narrow down one of the causes. If the Inspector is visible and I highlight more than 1 GameObject with a UITexture attached, several errors crop up.
Several from NGUIEditorTools:859
ArgumentException: Getting control 2's position in a group with only 2 controls when doing Repaint
Aborting
UnityEngine.GUILayoutGroup.GetNext () (at C:/BuildAgent/work/d3d49558e4d408f4/artifacts/EditorGenerated/GUILayoutUtility.cs:512)
UnityEngine.GUILayoutUtility.DoGetRect (Single minWidth, Single maxWidth, Single minHeight, Single maxHeight, UnityEngine.GUIStyle style, UnityEngine.GUILayoutOption[] options) (at C:/BuildAgent/work/d3d49558e4d408f4/artifacts/EditorGenerated/GUILayoutUtility.cs:305)
UnityEngine.GUILayoutUtility.GetRect (Single width, Single height) (at C:/BuildAgent/work/d3d49558e4d408f4/artifacts/EditorGenerated/GUILayoutUtility.cs:280)
NGUIEditorTools.DrawTexture (UnityEngine.Texture2D tex, Rect rect, Rect uv, Color color, UnityEngine.Material mat) (at Assets/Addons/NGUI/Scripts/Editor/NGUIEditorTools.cs:859)
NGUIEditorTools.DrawTexture (UnityEngine.Texture2D tex, Rect rect, Rect uv, Color color) (at Assets/Addons/NGUI/Scripts/Editor/NGUIEditorTools.cs:796)
UITextureInspector.OnPreviewGUI (Rect rect, UnityEngine.GUIStyle background) (at Assets/Addons/NGUI/Scripts/Editor/UITextureInspector.cs:69)
UnityEditor.Editor.OnInteractivePreviewGUI (Rect r, UnityEngine.GUIStyle background) (at C:/BuildAgent/work/d3d49558e4d408f4/artifacts/EditorGenerated/EditorBindings.cs:279)
UnityEditor.Editor.DrawPreview (Rect previewPosition) (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Mono/Inspector/Editor.cs:309)
UnityEditor.InspectorWindow.DrawPreviewAndLabels () (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Mono/Inspector/InspectorWindow.cs:523)
UnityEditor.InspectorWindow.OnGUI () (at C:/BuildAgent/work/d3d49558e4d408f4/Editor/Mono/Inspector/InspectorWindow.cs:286)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/monoAndRuntimeClassLibs/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)
and sometimes another
The targets array should not be used inside OnSceneGUI or OnPreviewGUI. Use the single target property instead.
UnityEditor.DockArea:OnGUI()