It'd seem the encumbrance penalty calculation is somewhat bugged with 3.80 Stable.
New character, 221lbs (about 100.5kg), carrying 35.8lbs (16kg) incurs a 10% penalty. Most of the weight is from a fur overcoat.
Also noted, when carrying load at body weight, the encumbrance penalty is 84%.
It used be body weight +50% to incur a 49% penalty; any higher than that would bump the penalty to 100%.
Now exceeding the bodyweight+50%, incurs a penalty over 100% encumbrance. (123%-ish)