Upon dying the players items appear to be dropped before the player's motion for that tick have been applied. This means that at high speeds the players items will drop in a different location to their body.

Normally this is neither noticeable nor a problem (as the items are only a single tick behind the player); however this can cause problems with commands handling players dropping items on death, as the items are not where you would expect them to be.

I have included screenshots of tests I ran on this bug below.
In the tests I would automatically summon an armorstand at my position upon dying and also summon a small armorstand for each item dropped. All of this happened on the same tick as my death