In my relatively simple project (one bootstrapping main file, and one file with all the bulk of the code), I introduced a simple typo in an expression, and I got no reporting in any window about the error, either in the Haskell perspective or the Debug perspective. No error highlighting, no problem reporting in the problems window.
The Outline window is working, Hoogle is working, and HLint is working from the console. The debugger launches, and in the debug perspective, I can step through the code. So this is just about error reporting about the compilation process.
Am I missing something? If not, can you recommend where in the Eclipse source I might root around for something not starting up or processing data?
Why the source code? First look at the buildwrapper output for your project, in debug mode. You should be able to see the results of the calls when you make a change in the editor. First their the syntax highlighting then the outline then the GHC build. The errors should be reported there, then they bubble up to Eclipse markers. You first need to check if the proper error makes it back from buildwrapper, to see if the problem is in buildwrapper side or the eclipse side.
Same thing here: run the buildwrapper unit test and tell me the results.