DTA is really far far from being perfect.
Every time I try to use it, getting "DTA engine unexpectedly stopped". Also every time this happens, I have to manually delete hypothetical indexes created by DTA.
3 years ago I was getting this error in SQL2008, now I'm still getting this error in SQL2012 (of course with full updates and cumulatives applied).
And there's no solution to that. Some said, if you use temp tables this will happen. Some said, if you use functions not real tables, this will happened. Some said, if you use xml fields this will happen. bla bla bla.
No real explanation, no real solution.