One effect that could be causing some of these weird features is solid phase change. Excuse my wild speculation. I'm used to thinking outside the box, and if this doesn't conform to widespread terrestrial examples that 'obviously' have analogs on Mars, then I apologise in advance.
We know that at the Viking 2 site, ground frost was common during winter days.
There could be times when ground frost also occurs at Endurance (possibly during the colder nights). Just possibly, the conditions are right for the chloride and bromide salts within the regolith to cause surface interaction with surface frost. Other anhydrous salts, being hydroscopic, will absorb water, forming hydrates, which will subsequntly slowly lose their water of crystallisation. Magnesium sulfate is an example.
Now this may appear to be a problem, since liquid phase requires temperatures above -60 C. However in some cases there is a negative enthalpy of solution - the absorption of superoxide (perhaps a minute contribution) is a case in point. A negative enthalpy of solution effectively means that heat will be transferred to the environment during the reaction.
Now this is a long-shot, but a substance that absorbs water and gives off heat could form a pasty flow (surrounded by a frozen crust) under Martian conditions.
