gcc5.2 abi change -> compatibility guaranteed?

I have the following situation (Ubuntu 15.10 and Debian Testing)

I have Lib A which is compiled without cxx11 and a lib B that uses -std=c++11. B includes and links against A, A uses boost.

If i link B to A, the application a A created crashes during dynload. If i compile A without cxx11 or B with cxx11 everything works fine.

My question: as far i understood the ABI namespace add on should guarantee shuch kind of problem. Am i wrong here?

P.S. Furthermore i run the same setup on a debian stable (gcc 4.9) everything works here fine too.