The bug

/execute store ignores value validation, allowing you to set values which would be considered invalid when used in the respective command.

Partially relevant /r/Mojira discussion

Affected situations

• bossbar max
• bossbar value
• read-only scoreboard objectives

How to reproduce

bossbar max

1. Create a bossbar

   /bossbar add custom:test "test"
   

2. Try setting a negative maximum

   /bossbar set custom:test max -1
   

   → It fails as expected

3. Create a scoreboard objective and set a negative score

   /scoreboard objectives add test dummy
   /scoreboard players set value test -1
   

4. Try storing the score as bossbar max

   /execute store result bossbar custom:test max run scoreboard players get value test
   

5. Get the bossbar max

   /bossbar get custom:test max
   

   → It shows -1

Read only scoreboard objectives

1. Create a read only scoreboard objective and have it displayed on the sidebar

   /scoreboard objectives add health health
   /scoreboard objectives setdisplay sidebar health
   

2. Take damage or heal to update the score (see MC-111729)
3. Try setting a value for the health objective

   /scoreboard players set @s health -1
   

   → It fails as expected

4. Create a scoreboard objective and set a negative score

   /scoreboard objectives add test dummy
   /scoreboard players set value test -1
   

5. Try storing the score as value for the read-only objective

   /execute store result score @s health run scoreboard players get value test
   

   → Your health score changed to -1