Item display sometimes has a strong shadow when brushing from suspicious sand/gravel

Steps to Reproduce:
 
1. Use a brush on a naturally generated suspicious sand or gravel.
 
2. Watch closely at the item displaying while brushing.
 
 
 
Observed Results:
The item display that will pop when finished brushing sometimes has an intense shadding preventing from seeing the item's texture.
 
Expected Results:
The item display shoud not have a strong shadow preventing from showing its texture.