Google's John Mueller said in a Google Webmaster Help thread that you should avoid using special characters in your URLs. Specifically avoid using "commas, semicolons, colons, spaces, quotes, etc." in your URLs.
John Mueller said Google handles it find when these URLs are in your XML sitemap file or normal links but when they discover the links via HTML, it can be confusing for them.
John wrote:
I generally recommend avoiding special characters like commas, semicolons, colons, spaces, quotes etc. in URLs, to help keep things simple. URLs like that are often harder to automatically link (when someone posts in a forum or elsewhere), and hard for us to recognize correctly when we parse text content to try to find new URLs. When they're linked normally or submitted through a sitemap directly, they work as expected. However, when we try to recognize the URL in something that we crawl as a HTML or a text page, then we'll probably "guess" them wrong -- which is fine, since we've probably already seen them through the normal links & sitemap usage.
The most common issue is spaces in URLs, but it is rare to see many folks using commas, semicolons, colons, although, I have seen it.
If you do, John may recommend you 301 redirect the special character URLs to the more traditional URL format.
Forum discussion at Google Webmaster Help.
