i am the owner of the server future bird is playing on, we are finding that iron shovels are corrupting player inventories, we have not been able to track this down on our main tekkit server, but oddly enough they don't crash it's twin testing server. which we are able to use to remove the shovels and repair the playerfiles.
i am not the server manager for the tekkit server so if you want technical details it will take a bit to get them.