You can report any bug on our GitHub issues (I'll ignore any PMs and any bug reports not meeting prescribed requirements). Append a log file (client log - fml-client-latest.log, server log - fml-server-latest.log in log directory). Try to describe in detail what you have been doing when a bug occurred, what is expected behaviour. Please do not report bugs related to not completed features (which are usually not obtainable in-game without cheating - e.g. creative mode).