From the screenshots below:
The first will show me typing the command: /gamerule doTileDrops false, effectively making it so TNT blasts should not drop blocks.
[media]The second will show me blowing up TNT, and as you can see, it still drops entities.
[media]This bug should be reproducible by setting up a similar experiment. Thank you!
Cannot reproduce, perhaps a command block/function is setting it back to true.