Can't shoot through see-through grates on one wall

[Xfing]

It seems to be a one-shot problem - in one particular instance I can shoot through one side of a grate, but not through the other - it just stops my shots as though the see-through texture was absent. Any idea as to what this could be? I even copied the area from a level where it worked fine, upon pasting nothing can be done to remedy this, even manually remaking the blocks from scratch and reinserting the wall.