Why is it so complicated to walk on stopped escalators? Is it because it feels like walking back in time? Or are the riffle telling the feed not to move? Or is just because you're loosing your rythm? I don't know - fact is: most people I watch avoid stopped escalators if there is a normal staircase next to it.
Stopped escalators
I like to step on
I like to step on escalators. 
So I even use them instead of normal staircases even if they're stopped.
They usually just feel nicer.
Although I have to admit it's kinda strange feeling to "climb up" those high steps.
Size and scale.
The size of the treads is all wrong, they aren't designed for walking up so it just feels unnatural compared to a normal sized set of steps. Also the height of the handrail is slightly wrong since it's designed to be held as you stand stationary with your hand to the side, whereas a normal staircase handrail is designed to be grabbed with your hand slightly forward.
I avoid them because they
I avoid them because they are unpredictable - maybe it just starts to move when i am stepping on it. In the worst case, I would lose balance and fall down given my poor equilibrium sense. I prefer ground under my feet that doesn't start and stop moving when it feels like it. A normal staircase is perfectly trustworthy - it won't do anything unexpected.
rise to run ratio
Escalators have a different rise to run ratio then stationary steps. When an escalator is moving, the rise to run ratio is less then when it is stationary. When it is stopped, the ratio is wrong.