Where do extra spaces come from before lines when rendering a multiline string in a textarea?

Question

Ruby on Rails

Good afternoon, I took Rails5 for a new project and immediately stumbled upon a problem.
In short, there is a model with a text string field that needs to be edited in the textbox. Form code:

.form
  =form_for article do |f|
    .form-group
      =field_label f, :text, true
      =f.text_area :text, class: %w(form-control), rows: 20, placeholder: t('placeholder.article_text')

On Create, everything is saved normally, but on Edit, several spaces appear before each new line in the textbox.
Empirically reduced the exploit to the simplest. Even a simple test.html.erb file:
<textarea><%= "a\nb\nc" %></textarea>
It looks like this on the page:

Even a simple <p><%= "a\nb\nc" %></p>one also pushes a bunch of spaces, just the browser trims them (visible in the developer console)
What to do and how to deal with it? Is this a bug (feature) of the fifth rail or what?