Nihil Obstat

Hello, I experienced exactly the same problem on my server. Putting stuff in it, deleted it after a relog, taking stuff out of it, duplicated it after relogging. It was always put back to the exact same things I had in the knapsack from before the server update. I updated from 1.0.10b to 1.0.12a. My solution (at least it works for me): 1. Log into the server and take all your stuff out of your knapsack. Put it in your inventory or a chest, otherwise you will lose it. 2. Log out and log in again. Your stuff should reappear in your knapsack. Now delete it all. 3. Log out. Do not log in again. 4. Download your player.dat file from your server. It's located in your world/players folder. 5. Open your player.dat file in NBTExplorer. Easiest way is via drag and drop. 6. Look for the folder 'ForgeData' and expand it. 7. Inside you will find another entry called 'TConstruct.Knapsack: xx entries' 8. Expand it and select all the entries in it. 9. In the top bar in NBTExplorer click on the red cross (Delete Tag) to delete all entries. 10. Do not exit NBTExplorer yet, but again in the top bar click on the disk icon (Save All Modified Tags). 11. Exit NBTExplorer. 12. Upload your now modified player.dat file to your server. 13. Log into your server and test if your knapsack works again as intended. Remember to always backup files you are tinkering with. Hope this helps. P.S. If you don't know NBTExplorer, google for it using 'minecraft nbtexplorer' as search terms.