Command block and tp command bug

It's a teleporting bug. So when I made some tests with the command block for my map, I noticed the bug.
So i made a hallway, 2x1, and 8 blocks long. On the eight block I put an pressure plate connected to a command block. The command block teleports me back to the second block. And when you walk trough the hallway it teleports you back to the beginning. But! when i was running trough it, it teleported me twice, and then let me trough. The third time it didn't work. I tested it again and again and on the 3 or 4 try it lets me trough without teleporting me. So could you take a look at it because this hallway should be unable to go trough because of the /tp.