It looks like in the last hour a change was made to the API Explorer page, and now the drop-downs don't work. Did you finally sunset v1.3? because I don't see it there anymore, but try clicking in 1.4 the Classifications API and then try to select a method. No drop-down list appears for me.
Can somebody confirm? I've tried it on two different computers, and an hour ago it was all working.
-Craig