Well, a segmentation fault should not happen (obviously). There are (unavoidably) cases where it's possible for PHP code to cause one but merely starting a session certainly is not one of them.
It appears to have been logged, identified and fixed; however it isn't part of the current 5.3.0 distribution. It seems this wasn't picked up by pre-release testing 🙁
I don't know if you want to try with a dev build, so unless you're using 5.3.0-specific functionality, then using 5.2.11 instead until 5.3.1 is released may be the way to go.