Update: BaseHierarchySort is going to be obsolete in 5.4.

Steps to reproduce:

1. Open attached project
2. Open scene "TestScene"
3. Set Hierarchy sorting to "Test Alpha Numeric Sort"
4. Select "OpenMe" in hierarchy and press right arrow key to expand it
5. Actual result - Notice that "WatchMeOpen" is expanded

Expected result: "OpenMe" is expanded

Used sorting is found here: http://docs.unity3d.com/ScriptReference/BaseHierarchySort.html

Note: Expanding using mouse (by clicking on triangle near object) works as expected
Note2: Using built-in Alphabetical sort works as expected

Regression introduced in 5.3.0b4, prior to this version, whole hierarchy would become invisible once doing step 4, so this might have regressed before that.