Game reset player's selected item slot when player died

When player died, their selected item slot always reset to first instead of keep it and recovery.

It's not different for exit and re-join world, the latter will keep selected item slot when exit world, and recovery selected item slot when re-join the world.

It's exist VERY VERY LONG, at least started from year 2013, but it's usually ignored.

Step to reproduce

1. Select another hotbar slot (not first slot);

2. run /kill;

3. Press "Respawn".

Expected result

Player's selected item slot will keep when died.

Observed result

Game reset the player's selected item slot.