Tag separator in tag page URL

I have created a website which navigation uses tagging and pagination.
I am wondering if there is a way to change the URL construction for the tag pages.

For the first page, the URLs are built in the following way:

Links appearing in the pagination navigation, however, are not built the same way:

This creates duplicate URLs for the same pages, which is not recommended for SEO.
In any case, it would be better to have - instead of + or %20 as separators

Is there a place where I can modify the construction of the URLs?

In Ditto 2 all URL creation requests go thru the buildURL function in ditto.class.inc.php. You will probably want to try removing the urlencode functions.