MCPE IOS 0.8.0 invincible grass and melon in creative

In creative, it seems grass blocks and melon blocks have the blast resistance of obsidian.

I was trying to blow up stuff, for example the terrain, but grass never was destroyed. I did a series of blast resistance tests for different materials and it turned out melon blocks and grass blocks are indestructible with TNT. However, after accidentally detonating very large amounts of TNT by accident, and dropping to 2 FPS for a couple seconds, I found that grass once again became destructible. Later on, the grass became invincible again, but melons became destructible. This is the situation I am in right now.

To replicate the bug, please:
1. In a creative world, attempt to blow up grass or melon blocks.
2. If they are successfully destroyed, test blast resistance of other blocks as the bug may be picking random blocks.