Problems with My .htaccess file and the friendly URL

In my systems I am implementing this from the friendly URl since it seems unprofessional to see the extensions of the files and the variables that are passing through $ _GET, I have already managed to remove the extensions of the files by means of the .htaccess well, once the user enters his desk previously logged in I have this address:

http://localhost/test/casillero/usuario

here my htaccess file

<IfModule mod_rewrite.c>
Options +FollowSymLinks
RewriteEngine on
RewriteBase /test/casillero/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}.php -f

#Reglas para cambiar las extensiones de los archivos en las URL en los archivos principales
RewriteRule ^(.*)$ $1.php
RewriteRule ^registro$ frmregistro.php [NC]
RewriteRule ^login$ frmlogin.php [NC]
RewriteRule ^usuario$ escritorio_user.php [NC]

#Reglas para las URL amigables
RewriteRule ^([a-zA-Z0-9/_]+)$ escritorio_user.php?modo=$1 [L]
RewriteRule ^(.+)/(.+)$ escritorio_user.php?modo=$1&cas=$2 [L]
</IfModule>

here the menu bar where the user navigates

<ul class="nav navbar-nav">
                    <li ><a href="nvafactura/<?php echo $_SESSION['casillero'];?>"><span class="glyphicon glyphicon-list-alt" aria-hidden="true"></span> Facturas <span class="badge" id="facturaspendientes"></span></a></li>
                    <li ><a href="alerta#frmalerta"><span class="glyphicon glyphicon-bullhorn" aria-hidden="true"></span> Alertar</a></li>
                    <li ><a href="rastreo"><span class="glyphicon glyphicon-globe" aria-hidden="true"></span> Rastreo de paquetes</a></li>
                </ul>

What is my problem? When the user browses, for example clicks the link 'alert' gets this address in the url:

http://localhost/test/casillero/alerta#frmalerta 

Perfect! and so on when you click on the tracking link you get this address:

http://localhost/test/casillero/rastreo

Perfect! when you click on the link nvafactura you get this address:

http://localhost/test/casillero/nvafactura/DT24VZ-51

Perfect! because it is the format that I gave it in the file htaccess and it is bringing me the results of the database since through that link I am passing 2 variables $_GET .

Perfect! The detail is that when the system is in the last URL mentioned and the user wants to click for example on the link alert, it gets this address:

http://localhost/test/casillero/nvafactura/alerta#frmalerta

And if I give it back to crawling it gives me the following URL:

http://localhost/test/casillero/nvafactura/rastreo

Instead of giving me:

http://localhost/test/casillero/rastreo ó
http://localhost/test/casillero/alerta#frmalerta

And if I return to the link invoice gives me the following URL:

http://localhost/test/casillero/nvafactura/nvafactura/DT24VZ-51

I see that the system does not return to the base address once the user enters the link nvafacturas and causes me a problem in the system does not show me the pages mentioned in the links, how can I resolve this since I have tried and I have not gotten, I read here a post that had a similar problem but I could not solve my problem, greetings.