> but it sounds like it's a fun, emergent gameplay mechanic

That you do less damage if you do a certain movement sounds like fun, emergent gameplay? That's not how I understand either of those terms, but of course, every player likes different things.

Surf maps in CS is actually a good example of an engine bug leading to game designers intentionally use it to design new experience, with the keyword being "intentional" since those map makers actually use that bug intentionally. For me that feels very different from engine bugs that don't add any mechanic, and instead just makes the normal game harder.