You'd think wouldn't you!

Technically this is just a visual issue, as the waze server is keeping track of speed in both directions. And if you are using routing, then the average or realtime (if another waze user has gone through the area recently), for that direction, will be taken into account.

Just by my observation, it appears that you can tell the directionality of a speed coloring, by which end the report flag is on. The report flag is on the start end of the speed coloring.

Now as far as the report trying to tell you what direction the report is for. This possibly could work, if the road segment is straight and on a N/S, E/W grid. But there are issue with roads with turns. Some of these need a little human touch to be able to say exactly which way the road travels.