execute with relative coordinates commands are forced to the center of the X and Z axis of the block the target is in, not the target itself

Note: this is not a duplicate of MC-63419 as the particle command alone can be moved anywhere on the X and Z coordinates.

Bug:
Any command (summon, particle) using execute with relative coordinates activates to the center of the block the target is located within.

Screenshot shows a Creeper locked in the middle of 2 blocks, I used this command

/execute @e[type=Creeper] ~ ~3 ~ /summon Creeper ~ ~ ~

Result:
The new Creeper summoned appears in the exact center of the block, instead of dropping overtop the original Creeper. Summon and particle alone without execute allow for decimal coordinates.

This is also evident by putting this command on a clock

/execute @p ~ ~ ~ /particle heart ~ ~ ~ 0 0 0 0

The particle is always in the center of the closest block to the player instead of the player (which should be that case using execute).

Another example is to move to the corner of a block, fly up and issue this command:

/execute @p ~ ~ ~ summon Item ~ ~-2 ~

The Item will always summon to the center of the X and Z axis instead of the player's location.