As of this feature request being completed, links pasted into the Insert Hyperlink dialog that appears when you click the Hyperlink button in the editor automatically go through some kind of URL-encoding, replacing non-ascii and certain other characters with percent-encoded versions. For example, if you paste
into the hyperlink box and click
OK, the link that gets inserted into the editor is actually a link to
This percent-encoding of characters works fine, and, as far as I know, does not break anything. However...
The Insert Hyperlink box also - destructively and, as far as I can tell, pointlessly - un-encodes certain characters in URLs, notably including the ampersand and equals signs, which many sites require to be percent-encoded when appearing as part of the data in a query string. That is, occurrences of
%3D in URLs pasted into the Insert Hyperlink box are replaced with
Examples of this breaking, or else undesirably modifying, links:
1) This valid Google search URL:
gets converted to this rather differently-behaving one if you paste it into the Insert Hyperlink box:
2) This valid URL from developers.facebook.com:
gets converted to this broken one:
Never un-encode any percent-encoded characters in a URL pasted into the Hyperlink box, ever.