Wow, that's new! I've never seen a quoted substitution URL before, and it's great to know that it works.
The usual solution is to use %20 for the space and use the [NE] flag on the rule, or to escape the space with a preceding backslash ( e.g. "\ " ). But quoting the string is easier and looks much more readable.
Using spaces in URLs is so problematical. They are often encoded as %20 and make URLs unreadable. Additionally, sometimes they become double encoded (where the % sign itself is encoded again) and that can cause all sorts of problems.
Can I suggest that you use hyphens or dots between words? Is there a good reason why spaces have been used? If the URL hasn't yet been indexed, I would strongly suggest that it be changed, to lose the spaces.
If it is a script that generates the pages from a database, then it is fairly easy to take the text that I assume you currently use for both the title and for the URL and add hyphens or dots between the words for whatever you are going to use for the URLs and for the links to those pages.