I do not know if anyone has reported this, but it seems that there is a problem with the side-ramps on Walls NF [both GDI and Nod side]. It seems to be possible to "climb up" the Wall with tanks. Yesterday on Constructive Tyranny's Marathon srv., Nod Flame Tanks have scaled the GDI Wall's side ramp near the Weapons Factory, from the outside. I asked the other players of the GDI team - others had witnessed this also at least in two instances.
Today, (on the same server) while playing on the Nod team, a whole battalion of GDI tanks (primarily Medium Tanks) have also done this "trick" en masse. I witnessed numerous players (some from the Leaderboard's first page) express their concerns regarding this phenomena in the in-game chat, as this is a regular map on many servers, and a most popular one at that...
Should this issue been reported previously, please take the liberty of closing this topic.