If the page title contains an ampersand, Inputbox generates the edit url with %26amp%3B instead of just %26, usually resulting in a server error; but has been reported as generating the page title truncated at the ampersand.
E.g. on en.wikt, enter foo&bar and "Go", then pick the "Noun" button; generated URL contains &title=foo%26amp%3Bbar :
go to http://en.wiktionary.org/w/index.php?title=Special:Search&search=foo%26bar
I have not tested other things that might be escaped in a URL or other cases, code needs looking at.