WordPress MU Domain Mapping Weirdness

Hi guys,

Normally I can get most of my answers off the newsgroups but I am a bit stumped on this one.

Installed WordPress Multisite with Domain Mapping. Everything is working fine only when I attempt to access my test domain https://www.lincolnbarros.com it redirects to my main hosting site on the signup page:
https://www.designntech.com/wp-signup.php?new=lincolnbarros.com

Yet when I put in lincolnbarros.designntech.com it redirects to https://www.lincolnbarros.com.

Now, in the same browser tab. I can put in https://www.lincolnbarros.com and get the desired site, but if I open a new tab I get the above signup page.

My .htaccess is exactly as specified by WPMU. I’ve pasted it below for your perusal:

#Turns the rewrite engine on.
RewriteEngine On

## Begin WordPress Mod_Rewrite Rules
#RewriteBase /
#RewriteRule ^index\.php$ – [L]

# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ – [L]
RewriteRule . index.php [L]
## End WordPress

P.S. Have to use WP 3.1.4 for the interim because my service provided (www.brinkster,com) can’t update my PHP version at present.