Horizontal line missing in png format
I have a graph on which (among other things) I've drawn the horizontal line y=1.
There appears to be a problem with this line and whether it appears when exported to png format.
If the x-axis : y-axis ratio is 1:1, the line appears in the exported image, as expected. But if I change the x-axis : y-axis ratio, the line disappears when the ratio goes to 10:1 and above.
Has anybody else experienced this problem and does anybody know a solution to it?