An inconsistency that I've noticed is that unlike other entities with health item entities don't receive a 0.5 second period of immunity after taking damage.

Steps to reproduce

Create a setup like this and place a lever in the middle

Run this command while near the item:

/data get entity @e[type=item,sort=nearest,limit= 1] Health

Flick the lever and run the same command again and notice that it's health has decreased by 2

Further experimentation can be done by using repeaters to add delay up to 0.5s between the tnt to see that the outcome is the same even without the blasts being processed in the same game tick.