An unexpected result on fitting

[shunruo]

I was doing curve-fitting with following data (json array)
data.json

It's very close to a straight line, but I've got a line with opposite trend, see the picture

with set order=2, [ y = -1.660432 + x*-9.694904+x^2*0.000240]
but it is okay after removing an element of the array. or, adding extra element also got correct result.

(add a point, { "X" : -112, "Y" : -1082.244})