well they seem to be puzzled by the parodox.
"Three other sets of observations by Phoenix, in addition to the terrestrial permafrost analogy, give reasons for expecting to find thin-film moisture in the soil.
One is the conductivity probe's own measurements of relative humidity when the probe is held up in the air. "The relative humidity transitions from near zero to near 100 PERCENT with every day-night cycle, which suggests there's a lot of moisture moving in and out of the soil," Zent said.
Another is Phoenix's confirmation of a hard layer containing water-ice about 5 centimeters (2 inches) or so beneath the surface.
Also, handling the site's soil with the scoop on Phoenix's robotic arm and observing the disturbed soil show that it has clumping cohesiveness when first scooped up and that this cohesiveness decreases after the scooped soil sits exposed to air for a day or two. One possible explanation for those observations could be thin-film moisture in the ground."
Possibilities... its all on the lander leg... 
another.. the probes sensitive nature is fooled by the static soils
or moisture sinks as in Under rocks, or shade, not in the sun.
as a whole it seems very positive, they expect to find microbes using the vapor trails.
