When you lower your max hp by holding an item, for example

/give @p stone{AttributeModifiers:[{AttributeName:"generic.maxHealth",Name:"233",Slot:"mainhand",Operation:0,Amount:-10,UUIDMost:11,UUIDLeast:11}]} 1

This time your hp is actually 20 unless you refresh it by taking damage or being heal.
I was trying to refresh my hp by adding a instant heal effect.

What I expected to happen was my hp was lowered to 10 and nothing else happened.

What actually happened was things like I suddenly lose all of my hp and regained instantly, and "You died" screen displayed. When I click "respawn" button, nothing was happened.

Steps to Reproduce:
1. Ensure your hp is 20, and your game mode is survival or adventure.
2. Execute this command and hold the given item.

/give @p stone{AttributeModifiers:[{AttributeName:"generic.maxHealth",Name:"233",Slot:"mainhand",Operation:0,Amount:-10,UUIDMost:11,UUIDLeast:11}]} 1

3. Execute another command to add effect.

/effect give @p minecraft:instant_health 1 0

4. Click the respawn button, then you will find nothing happened.