Drawing a plot with flat y values gives wrong tick mark for y axis.

Example:

Plot.plot({
  marks: [
    Plot.line([
      {x: 0.0, y: 0.5},
      {x: 1.0, y: 0.5},
      {x: 2.0, y: 0.5},
      {x: 3.0, y: 0.5},
      {x: 4.0, y: 0.5},
      {x: 5.0, y: 0.5},
      {x: 6.0, y: 0.5},
      {x: 7.0, y: 0.5},
      {x: 8.0, y: 0.5},
      {x: 9.0, y: 0.5}
    ], {x: "x", y: "y", tip: "xy"})
  ]
})

Result has tick mark 1 at the level of the line. The tip shows correctly 0.5. (Same example with y-values at 1.5 seems to give 2 as tick mark.)

(Tried to browse through the issues to see if this has been reported already but didn't find matching ossie.)