When you make a classic one tick redstone clock using redstone block "◘" comparator "C" 3 redstone "+" and a command block "☼" which is one block lower:

☼ + +
__+ C ◘

The command block stays always powered no matter how you connect it to the clock despite the fact that there exist much faster clocks using redstone block placing which work.

This might not be a bug but I can't figure out why it doesn't or shouldn't work