Devs didn't say it's bug, at least I couldn't see it. Can you show us where it is written so? Thanks.
You might as well say that the fact pounce deals no damage in the first second after firing a barb isn't a bug.
You might as well also say that the fact if you noclip above a solid slick surface and turn it off just above it without moving, the fact that your character bounces up and down isn't a bug either.
Also, the mara jump bug is clearly visible if you turn on the speedometer, preferably setting it to
horizontal speed (not verticle) and stick the the corner of a room, where you won't move. The speedometer will show up bouncing around 500ish if you do it correctly, even if you don't seem to move.