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implicit_plot shows wrong equation at edge of plot

I'm trying to implicit_plot a straight line, but am getting erroneous results when the line is at the edge of the plot region.

When I do

x,y = var('x y')`enter code here`
implicit_plot(y==2, (x,-0.1, 2), (y, -0.1, 2))

I get a plot with a vertical line at the right edge. (Unfortunately as a new user I can't post the image.) This is wrong since y == 2 should be a horizontal line at the top edge.

If I change the value slightly and do

implicit_plot(y==1.9), (x,-0.1, 2), (y, -0.1, 2))

I get a horizontal line near the top of the graph, as expected.

I also get correct results if I plot y==2 with ranges (x, -0.1, 2.1), (y, -0.1, 2.1) so that the line is not exactly at the edge.

Is this a bug that I should report, or is it somehow expected behavior?