For some entities Motion gets always calculated regardless of value

It seems like for some entities Minecraft is constantly calculating their Motion regardless of the value.

I am not sure if this is really the case for 0, but at least any number below or above 0 gets constantly changed.

Affected Entities (where it seems to happen):

• Items
• Minecarts
• Boats

While the effect is not so "extreme" for Items because the factor seems there pretty high, it creates unnecessary calculations for Minecarts and Boats.

Example:
Thrown item after about 2 minutes:

Motion:[0:-1.117E-321d,1:-0.0d,2:-8.45E-322d]

-1.117E-321d is an incredibly small number and has probably no effect at all, but the game still keeps calculating it.
Note: It either stops at Motion:[0:-4.9E-324d,1:-0.0d,2:-4.9E-324d] or this is the smallest number which is not 0 possible to represent with a double variable.

How to reproduce:

1. Throw an item
2. Run /entitydata @e[type=Item,c=1] {} a couple of times after waiting some time

Notes:

• This might be also the bug, while standing on a boat causes the player to constantly change his Y position
• For mobs it seems like -0.0784000015258789d is the smallest number for the Y Motion