The "%20" is a replacement for the space character in a name, and so It looks like the issue is both due to Craft & Vision using white spaces in their file names, as well as the browser using "%20" to validate the name. This filename problem seems to happen on certain browsers such as Safari, but it doesn't happen when downloading using Google Chrome.
At this point, possible solutions (while not ideal) are to:
-Change the "%20" to white spaces while downloading the file
-Use a different browser for downloading (such as Google Chrome)
We realize that these are short-term solutions, and will look into our naming conventions. We do appreciate your continued support of Craft & Vision and hope that in the meantime, you'll find one of these workarounds usable.