URLEncode() encodes the unreserved characters '-', '.', '_' - see http://en.wikipedia.org/wiki/Percent-encoding#Types_of_URI_characters
this creates a problem when communicating with systems that adhere to standards, e.g. Twitter API.
this is likely due to compatibility with ACF which does the same in URLEncodedFormat()
ACF, however, does not even have a URLEncode() function, so IMO we can fix this without repercussions, if we leave the old function unchanged.
another options is to add a flag, but since URLEncode() is not supported by ACF there really is no compatibility issue here.