Inconsistent implementations
For example, when specifying a change of image from small to large based on viewport size, some browsers will switch to the large image when the viewport is 1px larger than the small image’s preferred size, others will switch to the large image only when the viewport favored by the large image is fully matched.
In summary, browsers are split into two camps: those that favor higher quality images where possible, and those that favor smaller downloads where possible.
Inconsistent implementations