I have found that when I Create New Item from Current Page of a pdf that has a space in its name Zotero replaces the space with "20" (%20 is the url code for space) and indicates this in the Filename. The Title more often than not reflects the name sans "20" and when I drag it from Zotero to my desktop it's name is that given by the filename (no surprise there).

My question is why is zotero adding the 20 and not %20?

Ideally I'd prefer it if Zotero didn't transform the space, but perhaps this is asking too much.

Here's a page on which I have found a bunch of pdf's whose name includes one, or more, spaces:
http://www.usaswimming.org/usasweb/DesktopDefault.aspx?TabId=87&Alias=Rainbow&Lang=en