To reproduce:
1. Open user's attached project, in Project window, select sprite atlas MYATLAS
2. While MYATLAS selected, drag Tree sprite from Project window onto MYATLAS Objects for Packing area (in Inspector window)
3. Repeat step number 2, check Inspector window's debug mode - second sprite is not added to array
4. Add Tree sprite (located in New Folder in Project window) to MYATLAS, check Inspector window's debug mode - sprite is added to array

Expected: sprites with identical names are not added to Atlas under any circumstances
Actual: sprites with identical names are added to Atlas as long as they're not in a same folder

Reproduced in: 2017.1.0b6, 2017.1.0b9, 2017.2.0a3

Note: feature not available in earlier Unity versions
Note: since Sprite Packer has indexed sprite names (meaning they will be used as pointers to return the wanted sprite), it should not allow identical entries to a sprite array