Steps to replicate the issue (include links if applicable):

• Enter to revision comparision (diff) of page in non-main namespace
• Move slider multiple times (navigate through revisions)
• Look at URL in browser bar

What happens?:
%25 is added to the URL next to : (encoded as %3A after opening Slider box) every move of slider. The title attribute in the URL could like this: Wikipedia%252525253A and longer.

What should have happened instead?:
No change in encoding should be made and no unnecessary characters should be added. Percent sign should not be encoded if it is used to provide encoded character.

Impact
The URL itself does not broke anything - RevisionSlider works anyway and this URL can be visited. But it may complicate the URLs or broke something not tested. It indicates some errors with URL parsing or modifications which may affect other things using this "parser".

Software version (on Special:Version page; skip for WMF-hosted wikis like Wikipedia):

Other information (browser name/version, screenshots, etc.):