When using the an underscore in the front of a name no longer works for sorting in 4.7 and later. In 4.6 and prior if you added an underscore to the front of the name it would sort to the top of the list.
Image included to demonstrate.
1. Open UE4 Default Scene
2. In the World Outliner place an Undescore "_" in front of any asset in the middle or bottom of the list.
3. Click the "Label" tab twice to re-sort everything.
Results: assets that have been renamed with an underscore in front are treated as they are in alpha numeric sorting using the letter or number character as reference for sorting.
Expected: Using the underscore will sort the asset to the top/bottom of the list depending on the direction the tab is sorting. The underscored assets should shift to one end at least.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-15626 in the post.