Was reported privately by Dmitry Kovalenko.

When closing database on superclassic server in rare cases AV happens with following stack trace:

   ntdll.dll!RtlEnterCriticalSection() + 0x6 байт
   fb_inet_server.exe!Firebird::MemoryPool::deallocate(void * block=0x00000000047b7128) Строка 1942 C++
   fb_inet_server.exe!Jrd::Module::InternalModule::~InternalModule() Строка 77 + 0x1e байт C++
   fb_inet_server.exe!Jrd::Module::~Module() Строка 332 + 0x11 байт C++
   fb_inet_server.exe!Jrd::Module::`scalar deleting destructor'() + 0x14 байт C++
   fb_inet_server.exe!Jrd::Database::~Database() Строка 98 + 0x243 байт C++
   fb_inet_server.exe!shutdown_database(Jrd::Database * dbb=0x0000000004876aa8, const bool release_pools=true) Строка 5409 + 0x35 байт C++
   fb_inet_server.exe!purge_attachment(Jrd::thread_db * tdbb=0x0000000002f6f940, Jrd::Attachment * attachment=0x00000000047b71f8, const bool force_flag=false) Строка 5882 C++
   fb_inet_server.exe!jrd8_detach_database(__int64 * user_status=0x0000000002f6fb40, Jrd::Attachment * * handle=0x00000000005be2d8) Строка 2306 + 0x13 байт C++
   fb_inet_server.exe!detach_or_drop_database(__int64 * user_status=0x000000001280ba48, unsigned int * handle=0x0000000005244bb0, const int proc=410085592, const __int64 specCode=1) Строка 2270 + 0x19 байт C++