strange TIME behaviour

Can someone please explain to me why these two give different results?
The idea is to get the number of seconds past 00:00:00, so the second
one is obviously correct.

foo=> select extract(epoch from current_time);
   date_part
--------------
  42023.026348
(1 row)

foo=> select extract(epoch from cast(current_time as time));
   date_part
--------------
  60030.824587
(1 row)


Isn't current_time already a time? Why is the cast necessary?

Thanks.