That's definitely more semantics that I thought it contained, thanks for the clarification. However for the same reasons the debugging problems are probably more severe than I realized before.
As I said elsewhere, unless you believe the CoffeeScript compiler is introducing bugs into correct code, I'm not sure I understand your concern. Does the fact that C has different semantics from machine code generally make debugging C harder than debugging machine code? There is still a very close relationship between the CoffeeScript and the JavaScript — closer than, say, what you get with GWT or Closure Compiler. The ease of reading and writing and the reduction in source code length is worth the minor context switch to many people. It's easier to spot a bug in five concise lines than in 25 lines of mostly boilerplate.
For not using Javascript itself, that is widely understood across the programming community, that is not perfect but either not a disaster as a language, I would expect a lot more gains from a to-javascript-compiler. Here what I see is that there are a few semantical changes and syntax changes, but for me this is not enough to switch.
What I think the value of CoffeeScript could be is to show how Javascript could be improved in the next versions.
