Like I stated above, I've only used it once thus far but have a couple hundred miles worth of swimming with a Swimsense. I've found that when the watch screws up and misses a length, its pretty much something I did wrong. I've read before that a strong push off the wall is important and I think that in longer sets its easy to push off a little light due to fatigue. I've also messed up the length if I glide too much as it also uses no moving time to indicate a turn.

Your interval time will still be accurate so you should be able to tell if the lap count is off and can be corrected, at least in SportTracks anyway.

modified to fix my dislexia