After mining blocks of coal, the area may need to be refilled  (to prevent hostile mob spawn, fill hole in floor, etc.).  Sometimes, when filling the area with cobblestone, the placed block will actually be coal ore which can be mined for additional coal.  I have not noticed this effect with other fill blocks, and the bug only appeared after the 1.16.0.60 beta release.

Steps to reproduce:

Mine large vein of coal ore, then fill cavity with cobblestone blocks

Expected outcome:

Cavity fills with cobblestone

Bug outcome:

Random fill blocks placed are actually coal ore.

I have reviewed the bedrock database, and can find no similar issue