Suspicious sand/gravel produce different loot in the same seed

The bug

Blocks of suspicious sand or gravel produce different loot even when using the same world seed.

How to reproduce

1. Create a world with seed 1

2. /tp 9293 65 -363 180 30

3. Break the gravel until you find some suspicious gravel
   

   

4. Use a brush on it

5. Take note of the items you get

6. Repeat steps 1-5 again

Expected result

You should get the same items both times

Observed result

You get different items