Note that this is an "internal rewrite", not an "external redirect". The URL does not change in the address bar, the user is not actually redirected anywhere.
Rewriting/redirecting to a relative path can be problematic and this is likely to be the cause of your problem when you change this to a redirect (by adding the R flag).
This can be resolved with the RewriteBase directive (which controls what path is used in a relative path substitution), however, I think it would be preferable to make the substitution root-relative instead. Or, to avoid any ambiguity, make it absolute...
Note that this is a temporary (302) redirect. For a permanent redirect you need to state the code ie. [R=301]. I've also simplified the RewriteRule pattern by removing the end marker (.*$ is superfluous).