Tom Kunich wrote:

I wonder if that
over-estimation of LT time was merely the delay of the heart and the
heart rate monitoring to catch up.

The paper gave two reasons:
1. HR drift
2. HR lag

One of the interesting things in that paper is the table that shows
average power output for each of the stages of what appears to be this
race:
http://www.cyclingnews.com/results/2.../regio00.shtml

Stage 1: 167km, 650m altitude gain, 2.7 W/kg
Stage 2: 164km, 1500m altitude gain, 2.9 W/kg
Stage 3: 84km 700m altitude gain, 3.8 W/kg
Stage 4 uphill TT: 13km, 450m altitude gain, 5.5 W/kg
Stage 5: 170km, 400m altitude gain, 3.2 W/kg
Stage 6: 160km, 200m altitude gain, 3.4 W/kg

Note the overall GC winner of that race.