Oops, ir+displacement = crash for me too.
Corona gives you results so fast that it wouldn't be a big issue doing tests with normal render. But crash happens often even with normal render (if there are materials with bitmap for displacement). Last stable daily, as far as i can see, is 15.02. It also crashes with IR, but at least normal rendering is stable.
And again, of to OT we go...
Maru, could you please confirm my other displacement crash report, about water level, it's also on Mantis.