On v1.0.0-rc2 and the demo site at the time of this writing, pasting into a /code block appears to be rendering the text as markdown outside of the code box instead of as code inside the box.
I don’t think it is only with markdown content in the paste. Here is a paste without markdown content but has the same result of showing up outside the code block:
Pasted text:
mark@box ~/test> ls -l
total 0
-rw-rw-r-- 1 mark mark 0 Nov 24 15:25 test.txt
mark@box ~/test>