Inventory bug
Continuous swapping of an item from the hand with an item of the same type from the inventory leads to either the Transaction failed error or a segfault (here is log from GDB: Thread 1 "AltCraft" received signal SIGSEGV, Segmentation fault. 0x000000000043bb40 in World::GetEntity(unsigned int) () ).
Though the current behaviour of the inventory, when new items don't stack with items in the hand, is strange by itself.
And the content of the hand remains even after death.
In fact, the inventory is completely broken. I stopped working on it, after some discrepancies between the protocol description and the server behavior. Inventory will be corrected and implemented after work on the placement of blocks and basic lighting.
At the moment it's better not to use it at all.