If there is a status effect on a player, AND the player is holding one or more items that glow (enchanted tools, enchanted books, potions, nether stars, etc.), the status effect timers will render only their "window", unless one of the following is true:
-the player has his mouse over an inventory slot containing an item
-the player has his mouse over an inventory slot in the same row, and arbitrarily far to the right of the last glowing item in the inventory
-the player has his mouse over an inventory slot in a row below the row containing the last glowing item in the inventory
These findings where shown to be true in both creative and survival, but not outside of fullscreen mode.
No screenshots could be attached because of another bug disallowing screenshots to be taken with GUI windows open (inventory, crafting table, command block, etc.)
EDIT: These findings are also true in windowed mode, but only if the player is NOT viewing an "item group" in the creative inventory (buidling blocks, decoration blocks, foodstuffs, etc.) The bug is still present in the "survival inventory" in creative mode.