Resolution: Works As Intended
Minecraft 1.12 Pre-Release 5
Windows 7, Java:1.8.0_25 64-bit
When giving a player a status effect, any currently applied effects are displayed both in the inventory gui of the player and on the top-right corner of the screen. However, giving a player a status effect while also setting hideParticles to true for that effect will only display that effect's status in the player's inventory.
To reproduce, use these commands in a creative world on the most recently affected version:
/effect @p minecraft:<effect1> 9999 0 true
/effect @p minecraft:<effect2> 9999 0
Choose two different effects for each command. You can repeat these with other effects for further confirmation.
The status of effect1 should only be visible in the inventory screen. The status of effect2 should be visible on both the inventory screen and in the top-right corner of the screen.
See attached image where multiple effects are applied, but only 2 are visible outside of the inventory screen. These 2 effects were not set to have particles hidden.