There’s a spot in bm_c1a2a where an invisible wall prevents me from shooting a houndeye (see screenshot; includes position data). If I’m not supposed to kill it at that time, I’d suggest another solution because placing an obvious and confusing invisible wall at such a spot is always the worst solution (IMO). Making the houndeye appear there after reaching a certain area on the map might be a solution.
This houndeye at that point in the level is meant as a bit of a gag (as it’s sitting there watching the TV). You do actually end up being able to kill it a bit later once you get to that next area.
Though I agree, there’s no real reason to not let you kill it there, other than the devs not wanting the player to be a heartless dick with interrupting its favorite show.