Quartus 11.1 incorrectly compiles the design

I suggest you try to build in a signal tap to examine and try to isolate what's failing.

So far I haven't had any issues with 11.1 but it may be very specific issue with the code you are compiling.

If you can isolate it down to a single section of code, that's in error, you can open a service request to see if you can get a hotfix for it.

I would also double check any false path statements. It may be that the timing across a "false Path" is really critical, and the to routers just placed the logic differently, causing it to run or fail.

Pete