Glided Blackstone drops itself when which is mined, meanwhile sometimes it also drops Goldden Nugget

I noticed this on a video:
https://b23.tv/BV1Yf4y1U7aW
Watch from 2'33".
I think it should have the same behavior like Gravel, it shouldn't drop itself 1ce it drops Goldden Nugget.
As usual, this issue is used 2 let me know if this is a feature. If so, close this as WAI or Invalid.