How to redirect correctly a root domain to a subdomain in a subfolder?

Question

The next .htaccess code redirects example.com (from /public_html root folder) to the subdomain1.example.com (to /public_html/subdomain1 subdolder) and an old page register to a new one at subdomain1.example.com/enroll. So far so good! But, I have also a subdomain subdomain2.example.com (in the /public_html/subdomain2 subfolder) that instead of his normal URL is redirected to the subdomain1.example.com/subfolder2, that not exists. Why this happens and how to avoid this?

Options +FollowSymLinks
RewriteEngine on
RewriteRule (.*) http://subdomain1.example com/$1 [R=301,L]
Redirect 301 /register http://subdomain1.example com/enroll

Answer 1

This is the adopted answer, thanks to @anubhava:

<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^(www\.)?example\.com [NC]
RewriteCond %{HTTP_HOST} !subdomain.example.com [NC]
RewriteRule ^(.*)$ http://subdomain.example.com/$1 [R=301,L,QSA]
</IfModule>

Sourse: https://stackoverflow.com/a/19323457/1354580