This isn't really a bug.
Through trade signs some names are too long to be able to use; a few that I have come across:
Dark Prismarine - short verison: dprism
Red Nether Brick - short version: rnbrick
Nether Brick - short version: nbrick
Smooth Stone - short version: sstone
Nether Warts Block - short version: WartBlock or shorter still WartB
Dried Kelp Block - short version: Dkelp
Edit, found a few more (sorry to add to the work load):
Terracotta - shortname: tcotta
Light Gray Terracotta - shortname: lgcotta or lgclay