Redmine

In render_tabs method, when I click on next tab or previous tab button, form is submit instead of switching tab.

I think you should change

  <div class="tabs-buttons" style="display:none;">
    <button class="tab-left" onclick="moveTabLeft(this);"></button>
    <button class="tab-right" onclick="moveTabRight(this);"></button>
  </div>

to

  <div class="tabs-buttons" style="display:none;">
    <button class="tab-left" onclick="moveTabLeft(this); return false;"></button>
    <button class="tab-right" onclick="moveTabRight(this); return false;"></button>
  </div>