I can confirm for wooden trapdoors. See the attachments. The hole closer to the cannon is the 1.8 range. The hole farther is the 1.7 range. The 1.7 hole is larger due to two shots being fired.
As of 1.7.4, 1.7.5, and maybe 1.7.2, this is happening again.
EDIT: Could the resolved status be removed?
EDIT2: Any type of firework (Blank firework rocket is untested) can cause the bug as long as it leaves the loaded chunks.
I can confirm for wooden trapdoors. See the attachments. The hole closer to the cannon is the 1.8 range. The hole farther is the 1.7 range. The 1.7 hole is larger due to two shots being fired.