Comment 5 for bug 188649

It depends on what you consider as "intended behaviour". Actually, the result after flipping horizontally is the same as dragging the X vanishing point to the right and the Z vanishing point to the left - which visually amounts to "turning" the box around a vertical axis so that the back sides come to lie in front. I agree that this is probably counterintuitive at first sight but it's consistent within itself.

However, I think flipping should indeed work as you described since most users will expect it that way. Since this needs a bit of tweaking, it may take a while before I get around to correctly implementing it (first experiments revealed some problems I need to get sorted out), but it's on my to-do list.