Selectors don't work in command blocks with /tp command

When I tried to put the /tp with the @p selector in a command block, it didn't work. I tried again with the @a selector, which still didn't work. The same was with @r and @e. My own name didn't even work! But strangely enough, in chat, it worked perfectly. I tried a few other commands, which worked fine. Was there a change to the /tp command or this really a bug?