Taking Lethal Damage with Negative Max Health Only Sort of Kills the Player

I was testing custom items created using a command block. I created an item that had "Max Health -18" and held it, then took damage from a medium-sized slime. I "died" and got the death screen. I clicked respawn, but instead of sending me to spawn, it just closed the death screen and my game continued. My inventory picture showed Steve? standing diagonally with a slight red overlay, as if he was just about to die. The game, to my knowledge, operated normally during this time. My next death was a normal one, which sent me to spawn and reset my hearts.

To recreate:

1. Place a command block in creative mode

2. Enter the following as a command:
/give @p minecraft:brick 1 0 {AttributeModifiers:[{AttributeName:"generic.maxHealth",Name:"generic.maxHealth",Amount:-18,Operation:0,UUIDLeast:111112,UUIDMost:1111}]}

3. Activate the command block to give this item to the player

4. Switch to survival mode and hold the item

5. Begin taking small amounts of damage until death