Rails form keep sending old values after error - ruby-on-rails

Question

I have a form that for some reason always keep same values after error.
For example, if I enter name that already exists, it will get me an error and at the same time it will keep sending old value even if you change it (so you have to refresh page and lose all changes to actually resolve error).
= provide(:title, t(:create_task))
.center
= form_for :task, url: tasks_path do |f|
= render 'shared/big_flash'
= render 'task_error_messages'
.row.text-center
.col-lg-10.col-lg-offset-1.col-md-12.col-sm-12.col-xs-12
.jumbotron
%h2= t(:create_task)
.row
.col-lg-6.col-md-6.col-sm-6.col-xs-12
= f.label t(:par_task_name)
%i{class: 'material-icons text-muted', rel: 'tooltip', title: t(:tt_task_new_name)} info_outline
= f.text_field 'name', maxlength: 255, class: 'form-control'
= f.label t(:par_category)
= f.collection_select 'category', Category.order(:name), :name, :name, {}, {class: 'form-control'}
= link_to t(:btn_modify_categories), categories_modify_path, class: 'btn btn-primary btn-block', data: { confirm: t(:changes_lost_proceed) }
= f.label t(:par_task_type)
= f.select 'task_type', Task::TASK_TYPES_LIST, {include_blank: true}, {class: 'form-control', id: 'type_of_task'}
= f.label t(:par_score)
= f.number_field 'score', min: '0', step: '1', class: 'form-control'
.col-lg-6.col-md-6.col-sm-6.col-xs-12
= f.label t(:par_asset)
%i{class: 'material-icons text-muted', rel: 'tooltip', title: t(:tt_task_asset)} info_outline
= f.file_field 'category'
.description
= f.label t(:par_description)
%i{class: 'material-icons text-muted', rel: 'tooltip', title: t(:tt_task_description)} info_outline
= f.text_area 'name', class: 'form-control'
= f.check_box 'mathjax'
= f.label t(:par_mathjax)
%i{class: 'material-icons text-muted', rel: 'tooltip', title: t(:tt_task_mathjax)} info_outline
.row
.correct_solutions.col-lg-6.col-md-6.col-sm-6.col-xs-12
= f.label t(:par_correct_solutions)
#generated_correct_solutions
= button_tag t(:btn_add_correct_solution), type: 'button', class: 'btn btn-primary btn-toolbar', id: 'add_correct_solution'
.wrong_solutions.col-lg-6.col-md-6.col-sm-6.col-xs-12
= f.label t(:par_wrong_solutions)
#generated_wrong_solutions
= button_tag t(:btn_add_wrong_solution), type: 'button', class: 'btn btn-primary btn-toolbar', id: 'add_wrong_solution'
#close-ended_task{class: 'hidden'}
= f.check_box 'random', id: 'randomize_task'
= f.label t(:par_random)
%i{class: 'material-icons text-muted', rel: 'tooltip', title: t(:tt_task_random)} info_outline
#randomize{class: 'hidden'}
.row
.col-lg-6.col-md-6.col-sm-6.col-xs-12
= f.label t(:par_number_of_solutions)
%i{class: 'material-icons text-muted', rel: 'tooltip', title: t(:tt_task_no_random_solutions)} info_outline
= f.number_field 'no_random_solutions', min: '1', step: '1', class: 'form-control'
.col-lg-6.col-md-6.col-sm-6.col-xs-12
= f.label t(:par_min_number_of_correct_solutions)
%i{class: 'material-icons text-muted', rel: 'tooltip', title: t(:tt_task_min_no_random_correct_solutions)} info_outline
= f.number_field 'min_no_random_correct_solutions', min: '0', step: '1', class: 'form-control'
.btn-group.btn-group-justified.hidden-xs
.btn-group
= f.submit t(:btn_create_new_task), class: 'btn btn-lg btn-primary btn-toolbar'
.btn-group
= link_to t(:btn_cancel), '#', class: 'btn btn-lg btn-primary btn-toolbar'
.btn-group-vertical.visible-xs
= f.submit t(:btn_create_new_task), class: 'btn btn-lg btn-primary'
= link_to t(:btn_cancel), '#', class: 'btn btn-lg btn-primary'
And my tasks_controller.rb
def new
#task = Task.new
end
def create
#task = Task.new(task_params)
#task.user_id = helpers.current_user.id
if #task.save
flash[:success] = t(:task_created)
redirect_to new_task_path
else
render 'new'
end
end
Any idea what could be the problem?
I don't want to clean up fields after error, I want to keep them, just on next POST, send new values instead.