x轴转移到highcharts的中间位置

I'd like to upgrade highcharts to latest 2.3.5 version.

Everything seems to be good, except when all inputs for plot points for 'areaspline' type highcharts are zero values, x-axis shaded line got shifted to middle of the graph instead of showing in the bottom. In previous versions it shows in the bottom.

When inputs are non-zero values, x-axis shaded line shows at the bottom.

Could you please let me know the reason and possible solutions which avoid x-axis line shifting.

Much appreciated your valuable help.

Thanks,

Kiran