I believe the bolded bit is intentional, as the Street Sweeper is something close to an Easter Egg which has to be looked for.
edit
Here is how it looks currently:
Not so much a shadow but a brown object lying on a slightly different shade of brown surface. Can be nearly impossible to see when it's cloud's shadow passes over it..
But that's why it's an Easter Egg.
Ironically it might be slightly easier to see at nighttime as it stands out a bit more in my subjective opinion:
Does kinda look shadowish there, I agree. But, again as far as I know, this is intentional.
