Preservation level: Final leads to Quartus crash on re-run

I changed one partition from final to synthesis preserve, it wen't further but still crashed later on.

I think the final flow is kind of broken, which is sad because this is what I was planning to use to speed-up the big projects.

See new picture too.

Problem Details
Error:
Internal Error: Sub-system: QHD, File: /quartus/comp/qhd/qhd_database_impl.cpp, Line: 2057
validate_split_route check failed (see debug messages for more info):
            	snapshot:routed
	flat_vs_split:FAILED
	split_vs_flat:PASSED

Stack Trace:
  Quartus         0x111679: QHD_CHECK_DESIGN::validate_split_route(QHD_DESIGN const&, QHD_ENUM_IMPL<QHD_SNAPSHOT_BASE>) + 0x2e17 (comp_qhd)
  Quartus          0x58fe7: QHD_CHECK_DESIGN::fit_post_commit_design_check(QHD_DESIGN const&, QHD_ENUM_IMPL<QHD_SNAPSHOT_BASE>) + 0x3e (comp_qhd)
  Quartus          0x49568: FIT2_DATABASE_EXPERT_QDB::commit(bool, bool, bool) + 0xb3c (comp_fit2)
  Quartus          0x2c6b3: fit2_commit_fitter_netlist + 0x376 (comp_fit2)
  Quartus          0x50fb7: TclNRRunCallbacks + 0x47 (tcl8.6)
  Quartus          0x527df: TclEvalEx + 0x94f (tcl8.6)
  Quartus          0x52ad6: Tcl_EvalEx + 0x16 (tcl8.6)
  Quartus          0x26b81: atcl_tcl_eval(Tcl_Interp*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, bool) + 0x1df (ccl_atcl)
  Quartus          0x5c0a0: fit2_commit_result(Tcl_Interp*, bool) + 0x5f (comp_fit2)
  Quartus          0x3c132: fit2_fit_route_commit + 0x2a2 (comp_fit2)
  Quartus          0x50fb7: TclNRRunCallbacks + 0x47 (tcl8.6)
  Quartus          0x287d6: fit2_fit_route + 0x2fb (comp_fit2)
  Quartus          0x50fb7: TclNRRunCallbacks + 0x47 (tcl8.6)
  Quartus          0x527df: TclEvalEx + 0x94f (tcl8.6)
  Quartus          0xfa3a6: Tcl_FSEvalFileEx + 0x266 (tcl8.6)
  Quartus          0xfa4be: Tcl_EvalFile + 0x2e (tcl8.6)
  Quartus          0x2a8fc: qexe_evaluate_tcl_script(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) + 0x3de (comp_qexe)
  Quartus          0x2dd73: qexe_do_tcl(QEXE_FRAMEWORK*, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::list<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, bool, bool) + 0x4c2 (comp_qexe)
  Quartus          0x2ee7b: qexe_run_tcl_option(QEXE_FRAMEWORK*, char const*, std::__cxx11::list<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >*, bool) + 0x66e (comp_qexe)
  Quartus          0x6d1ec: QCU::DETAIL::intialise_qhd_and_run_qexe(QCU_FRAMEWORK&, FIO_PATH const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, char const*, std::__cxx11::list<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >*, bool) + 0x9c (comp_qcu)
  Quartus          0x6d638: qcu_run_tcl_option(QCU_FRAMEWORK*, char const*, std::__cxx11::list<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > >*, bool) + 0x343 (comp_qcu)
  Quartus          0x3421d: qexe_standard_main(QEXE_FRAMEWORK*, QEXE_OPTION_DEFINITION const**, int, char const**) + 0xba2 (comp_qexe)
  Quartus         0x40ad6c: qfit2_main(int, char const**) + 0x8c (quartus_fit)
  Quartus          0x4e546: msg_main_thread(void*) + 0x10 (ccl_msg)
  Quartus          0x4f764: msg_thread_wrapper(void* (*)(void*), void*) + 0x8c (ccl_msg)
  Quartus          0x1f568: mem_thread_wrapper(void* (*)(void*), void*) + 0x98 (ccl_mem)
  Quartus          0x10f3a: err_thread_wrapper(void* (*)(void*), void*) + 0x1e (ccl_err)
  Quartus           0xb7f5: thr_thread_wrapper + 0x15 (ccl_thr)
  Quartus          0x4f684: msg_exe_main(int, char const**, int (*)(int, char const**)) + 0xd8 (ccl_msg)
  System           0x22555: __libc_start_main + 0xf5 (c)
  Quartus         0x4062a9: _start + 0x29 (quartus_fit)

End-trace