That's not a security issue, it's a correctness issue.
The whole feature simply does not work.
The whole feature simply does not work.
Security becomes irrelevant if the whole Apache module is broken.
If you use RewriteCond as the basis of securing your website, that's a security issue for you.
If it's a security issue for a significant number of users, or if the documentation recommends using the directive for a security role, then it's also a security issue for the product itself.