Is rejecting URI's with base64 padding required?

[stevenroose]

RFC 4648 states:

The pad character "=" is typically percent-encoded when used in an
   URI [9], but if the data length is known implicitly, this can be
   avoided by skipping the padding; see section 3.2.

This does not imply that padding is SHOULD be left out (as currently five bells interprets it). However, it might be encoded using the percent encoded character (%3D), f.e. when it has been used in a URL, or it COULD be left out.