It's 100 degrees below zero there, even in daytime. Ice crystals mixed with sand wouldn't produce any stickiness under those conditions, would they? Unless they melted from the impact and residual heat of the lander and instantly froze in those shapes. I guess Spirit will find out in a few days.
BTW, have you seen the full video (10 minutes worth) of this mission at www.maasdigital.com? It's amazing. Unfortunaterly it's down now because of the traffic.