Server 0.4.12 crashed

[amadin]

In thread 7eff61e82700:
/build/minetest-KMJvg5/minetest-0.4.12+repack/src/util/pointer.h:279: void SharedBuffer<T>::drop() [with T = unsigned char]: Assertion '(*refcount) > 0' failed.
Debug stacks:
DEBUG STACK FOR THREAD 7eff535fe700:
#0 virtual void* EmergeThread::Thread()
(Leftover data: #1 MapBlock* ServerMap::loadBlock(v3s16))
(Leftover data: #2 void ServerMap::loadBlock(std::string*, v3s16, MapSector*, bool))
(Leftover data: #3 void ItemStack::deSerialize(std::istream&, IItemDefManager*))
DEBUG STACK FOR THREAD 7eff53fff700:
#0 virtual void* EmergeThread::Thread()
(Leftover data: #1 MapBlock* ServerMap::loadBlock(v3s16))
(Leftover data: #2 void ServerMap::loadBlock(std::string*, v3s16, MapSector*, bool))
(Leftover data: #3 void ItemStack::deSerialize(std::istream&, IItemDefManager*))
DEBUG STACK FOR THREAD 7eff60a80700:
#0 virtual void* EmergeThread::Thread()
(Leftover data: #1 MapBlock* ServerMap::loadBlock(v3s16))
(Leftover data: #2 void ServerMap::loadBlock(std::string*, v3s16, MapSector*, bool))
(Leftover data: #3 void ItemStack::deSerialize(std::istream&, IItemDefManager*))
DEBUG STACK FOR THREAD 7eff61481700:
#0 virtual void* CurlFetchThread::Thread()
DEBUG STACK FOR THREAD 7eff69481700:
#0 virtual void* ServerThread::Thread()
#1 void Server::Receive()
(Leftover data: #2 void Server::SendBlocks(float))
(Leftover data: #3 void Server::SendBlockNoLock(irr::u16, MapBlock*, irr::u8, irr::u16))
(Leftover data: #4 void ItemStack::serialize(std::ostream&) const)
(Leftover data: #5 void ItemStack::deSerialize(std::istream&, IItemDefManager*))
(Leftover data: #6 void ItemStack::deSerialize(std::istream&, IItemDefManager*))
DEBUG STACK FOR THREAD 7eff6fedc780:
#0 int main(int, char**)
#1 Dedicated server branch
#2 void dedicated_server_loop(Server&, bool&)
(Leftover data: #3 void Server::step(float))

Server from repository, linux 64 bit.