google charts api : wrong axis with LXY chart? - google-visualization

I'm trying to display some very simple data using Google Charts API.
My data are a serie of X,Y points:
(1,44) (2,46) (3,46) (4,43) (5,46) and (6,44).
X-axis : from 0 to 300, step 50
Y-axis : from 1 to 50, step 5
I should end up with a line almost in the top, to the left, of the chart (43-46 are near 50).
But here is what I get:
URL = http://chart.apis.google.com/chart?cht=lxy&chs=500x300&chd=t:1,2,3,4,5,6|44,46,46,43,46,44&chxt=x,y&chxr=0,0,300,50|1,0,50,5
If I change Y-axis, 1 to 100 (instead of 50), it's ok...
URL = http://chart.apis.google.com/chart?cht=lxy&chs=500x300&chd=t:1,2,3,4,5,6|44,46,46,43,46,44&chxt=x,y&chxr=0,0,300,50|1,0,100,5
I'm probably mistaking, but I can't find what is wrong.

If you add data scale the chart does show correctly.
http://chart.apis.google.com/chart?cht=lxy&chs=500x300&chd=t:1,2,3,4,5,6|44,46,46,43,46,44&chxt=x,y&chxr=0,0,300,50|1,0,50,5&chds=0,300,0,50

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