### A bug with solve()?

I'm trying to solve a toy linear system. Why does the result depend on the order of variables and on the repetition of the equations?

```
sage: var("x,y")
(x, y)
sage: solve([y==0],x,y)
([], [])
sage: solve([y==0],y,x)
([y == 0], [1])
sage: solve([y==0,y==0],x,y)
[[x == r3, y == 0]]
```