There is no glitch with the springs - it is just human error. I've even done it myself, more than once. In every case, it always turns out to be a mistake, and a visit was indeed missed.
141520 2012-08-19 03:43:51
141520 2012-08-21 00:03:35
As you can see, you missed a visit on the 20th by just 3 minutes 35 seconds.