lucy24 - 10:14 pm on Feb 26, 2013 (gmt 0)
are different URLs.
%2F and %2f are the same character. But not all functions can disencode both.
Google probably has its own internal function that regularizes [a-f] in encodings to [A-F]. (My logs apparently do the same-- or possibly it's the server itself-- because lower-case letters don't seem to occur.)
You shouldn't have encodable characters in the path of your URL anyway. Do you, or are they coming in from query strings? If so, I hope it isn't really %2F since that is the / slash, a character that doesn't belong in a query string. Either way, the path and the query should be handled separately.