Spaces in attachment filenames are converted to plus symbols when downloaded

After uploading an attachment with spaces, the file is downloaded with plus symbols instead in both IE and Firefox despite the MIME type being specified correctly. For example, 'New Text Document.txt' is downloaded as 'New+Text+Document.txt'. Confirmed with doc and txt file types.

http://localhost:8080/download/attachments/255/New+Text+Document.txt?version=1 downloads displays inline as New+Text+Document.txt and downloads with that filename, but this also occurs on other filetypes which don't display inline.

Response Headers - http://localhost:8080/download/attachments/255/New+Text+Document.txt?version=1
Server: Apache-Coyote/1.1
Last-Modified: Tue, 05 Sep 2006 07:35:19 GMT
Etag: "1157441719000"
content-disposition: inline; filename="New Text Document.txt"
Content-Type: text/plain;charset=UTF-8
Content-Length: 4
Date: Tue, 05 Sep 2006 07:41:36 GMT
200 OK