Arduino skips a beat...

Hello all. I have noticed something strange about my arduino. I have wired up my arduino dec the same as found in http://www.arduino.cc/en/Tutorial/ShiftOut . However, I did not use the capacitor as indicated on the latch pin. However, I'm not sure if that is at all my issue.

In short, my arduino is to execute a command once every second for example - light one of four LEDs.

So it'll start out like this: 1 - 2 - 3 - 4 with perfect cadence.

Then after maybe five or six times through the series it'll behave like follows: 1 - - -
Only the first led will be illuminated for four seconds.

Then it may do something like this: 1 - 2 - -, - 2 - 3 -, - - 3 - 4, 1 - - 4

Almost like it's having a brain freeze. Any ideas as to what may be causing this?

Schematic and code are needed.