Y axis range change in zoom after plot's refresh

I have this graph, with the property range defined in my yaxis.
When i zoom, all the axis changes ranges, ok for now.
I Have a event that refresh the graph data, THEN THE PROBLEM OCCUR.
The zoom stays the same, but the y_axis refreshs to initial size, like the image below ( The image is already zoomed!)!


then refresh, this happens:


This is normal? Any ideas to avoid that?