The bug

Let's take a look at the description for the "Birthday Song" advancement.

Have an Allay drop a cake at a Note Block

As you have observed, the in-game block "cake" has not been capitalized here. As you know, all in-game names should be treated as proper nouns, meaning that the correct stylization of this word would be "Cake".

• Translation string: advancements.husbandry.allay_deliver_cake_to_note_block.description
• Correct translation: "Have an Allay drop a Cake at a Note Block"

To reproduce

1. Grant yourself the advancement: /advancement grant @s only minecraft:husbandry/allay_deliver_cake_to_noteblock
2. Take a look at the Advancements menu: L
3. Under the Husbandry tab, hover over the icon for the challenge advancement Birthday Song (a noteblock)

Screenshots