Okay this is easy to reproduce. Have a couple of seed or gear vaults in your backpack. Put one down at your house. Now try to pick it up. Without using a glitch to do it, it can't be done. You have to move the remaining seed/gear vault to the bank or attic or place it in another house first. If you have any seed/gear vaults in your inventory when trying to pick another one up, it won't work.
