Something strange is going on here. This is fixed in really old changes. See for example
Change I36e6abf5: (Bug 39485) Encode params for ItemByLabel and ItemByTitle
Also there are old bugs about this; Bug 39485 - Add item link is broken on Special:ItemByTitle, Bug 42149 - Broken link in the invitation for users to update the item
Version: unspecified
Severity: major