Redirect 301 in .htaccess not accepting slash - wordpress

Question

I've got a WordPress blog that I'm trying to redirect to a new domain. The 301 redirect works, but it redirects to newdomain.comnew-post instead of newdomain.com/new-post.
Somehow, it's stripping out the slash. Here's the code:
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress
Redirect 301 /old-post/ http://www.newdomain.com/new-post/
What am I missing?

Answer 1

That shouldn't be happening unless there's also a redirect happening at the www.newdomain.com site. You need to make sure that isn't happening.
Another possibility is that maybe mod_alias (the Redirect directive) and mod_rewrite (all the rewrite rules for wordpress) may be interfering with each other. Both get applied to the same URI (when it's /old-post/ in the same URL-file mapping process pipeline. You could try removing the Redirect and stick to mod_rewrite, before wordpress' rules get applied at all. Try something like:
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteRule ^old-post/(.*)$ http://www.newdomain.com/new-post/$1 [L,R=301]
</IfModule>
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Answer 2

This may not be a solution for this exact scenario, but it did solve the problem where the slash character got removed from the URL it was redirecting to.
My code was similar to this:
Redirect 301 / http://www.newdomain.com
Redirect 301 /old-post/ http://www.newdomain.com/new-post/
The solution was to add a slash after the first line:
Redirect 301 / http://www.newdomain.com/
Redirect 301 /old-post/ http://www.newdomain.com/new-post/
One could also try:
Options +FollowSymlinks
RewriteEngine on
RedirectMatch 301 ^/old-post/ http://www.newdomain.com/new-post/