Interesting issue, and I'm not sure if it's with GRealm or the other mods, but the Bone Musket will fire an entire Endless (mod-crafted) Bullet Pouch in one shot, maybe a few shots at most. Just start firing, and the pouch in question will vanish quickly. It treats the Endless Musket Ball Pouch (the vanilla one) just fine, though. Tested this with @Joost8910 's Joostmod (boomerang and ricoshot pouches) and @Fargowilta 's (whichever mod adds crystal and ichor pouches).
I'm not bothered by it (using other gear), but I noticed it and thought I'd say something. Also of note: the Bone Musket does show the "Undead Weapon" tag when wearing Pelvic armor, but doesn't state what its undead bonus is.
Lastly, again with the golem vs walls question; I had it happen again in Hell, a golem down there knocked through a wall in a tower and flooded it with lava. Is this normal? Can all golems do this?
I don't know if its the cause of Banner Bonanza or of GREALM, but if I add a banner of GREALM (tested with Golem Banner and Myconid Banner) the banners neither draw in the rack nor tree leaves at the same height like the rack draw.
If I add some other banners in the rack, then everything works fine until the GREALM banners would draw in the rack. Then the banners in the rack an the leaves of the trees disappear, until again a "normal" banner gets drawn in the rack.....and repeat.
I already asked jopojelly and he said most probably there's nothing he can do about it in Banner Bonanza. So maybe you can have a look if it's an issue of GREALM?