Realtime Database - reading data gives wrong value if transaction is pending

[terreng]

[REQUIRED] Step 2: Describe your environment

• Operating System version: macOS 14.5 (23F79)
• Firebase SDK version: 12.2.0
• Firebase Product: database
• Node.js version: v20.13.0
• NPM version: v10.5.2

[REQUIRED] Step 3: Describe the problem

If a transaction is pending for a node, it doesn't show up when reading data for the parent node with .once("value", ...). I'm not sure if this is a bug or intended behavior.

Steps to reproduce:

For these examples, our database looks like this:

{
  "example_list": [
    "a",
    "b",
    "c"
  ]
}

This code works as expected:

let ref = admin.database().ref("example_list");

ref.once('value', (snap) => {
    console.log(snap.val())
});

Logs: [ 'a', 'b', 'c' ]

This code does NOT work as expected:

admin.database().ref("example_list/1").transaction((currentData) => {
    return currentData;
});

let ref = admin.database().ref("example_list");

ref.once('value', (snap) => {
    console.log(snap.val())
});

Logs: [ 'a', <1 empty item>, 'c' ]

Adding a transaction first, which seems like a no-op, actually causes the read to return a different result.