Heart rate data inconsistent over course of workout

Anyone else seen inconsistent heart rate data collected by the Watch Workout app, in that the sensor ranges from accurate (130 to 135 bpm) to inaccurate (60 to 85 bpm) within a single workout?

The data comes from the Health app (Health Data->Heart Rate->Show all Data) and was collected using 3 different Workouts to make sure the issue was not with a single type of workout. I first used the 'Other' workout for 25 minutes of warmup with weight machines, and the data collected seemed accurate (average bpm of 91 with a reasonable range for the type of exercise)

However, with a more strenuous exercise (that raised my heart rate consistently to the 130s verified by sensors on the gym equipment) using the 'Elliptical' and 'Indoor Walk' Workouts, the Watch sensors fluctuated between the 80s and a more accurate 130s without discernible reason.

For example, with the Elliptical Workout, the data readings showed a starting heart rate of 116 for 2 minutes (with many data readings in that time); then 3 minutes of readings between 59 and 62; then 2 minutes of 131 to 134; then 6 minutes of 83 to 86; then 3 minutes of 135 to 140. This was all recorded during the time the Elliptical machine was showing a consistent heart rate between 130 and 140.

To test another Watch Workout, I stopped the Elliptical Workout and started the Indoor Walk Workout, still using the elliptical machine, with the same results...1 minute of 135 to 138; 2 minutes of 78 to 83; 2 minutes of 133 to 135; 2 minutes of 98; 2 minutes of 131 to 137, and so on.

Of course, these inconsistencies reported both a false heart rate average and low calorie total for the 2 workouts.

BTW, the Watch was snug on my wrist, the sensor light was on, this issues occurred with both versions 1 and 1.0.1 of the Watch software, and while my arm was sweaty, no one seems to have reported any problems with sweat. I have restarted both my iPhone 6 and Watch without effect.