Assigning to loop variable fails silently

I am using Liquid through Jekyll 3.4.3, so this issue may not be current.

Variables assigned through {% assign %} can be re-assigned through {% assign %} or {% capture %}:

{% assign word = "three" %}{{ word }}
{% assign word = "not a number" %}{{ word }}
{% capture word %}something else{% endcapture %}{{ word }}

Output:

three
not a number
something else

However, variables assigned by {% for %} cannot be re-assigned:

{% assign test = 'one,two,three' | split:',' %}
{% for word in test %}{{ word }}
{% assign word = "not a number" %}{{ word }}
{% capture word %}something else{% endcapture %}{{ word }}
{% endfor %}

Output:

one
one
one
two
two
two
three
three
three

If this is the intended behavior, I would expect it to be documented and to see an error or warning generated when assigning to the (immutable) loop variable.

Reproduce the shown Liquid template to confirm whether loop variables remain immutable when reassigned with assign or capture. Then determine whether the intended result is documented behavior or an error/warning, and verify that the chosen resolution is reflected in the output and documentation.