Adding to a powershell array with only two elements does not work [duplicate]

Say I have the following code:

$roles = @("first", "second", "third")

$roles = $roles | Where-Object {$_ -ne "second"}       
$roles += "last"

$roles

This will result in the following output:

first
third
last

Just what I would expect. But if I take out the "thrid" element of the array, then it performs oddly. Here is the code I run (in VS Code):

$roles = @("first", "second")

$roles = $roles | Where-Object {$_ -ne "second"}       
$roles += "last"

$roles

This results in the following:

firstlast

(all on one line)

Is Powershell changing my variable to be a string when I pull out the second to last array? If so, how do I stop it from doing that? If not, what is going on here?

Why is my array all of a sudden working like a string?