I tried to search this question, but it seems to be rather specific.
The problem I have is the following:
We have a small SMP server in Minecraft and I set up an iron golem farm according to(only redstone in the hopper sorter system) and an automatic wheat farm according to (minecart running beneath the farm and a redstone circuit for the unloading as well as a hopper sorting system). Both farms work very well as long as a player is online.
Of course, they stop working after the somewhat 60s after the last player has logged out. So I went and read a bit about that topic and came up with the idea to send an item through a nether portal every 45s via a piston/hopper clock plus a dropper. This kinda seems to work, since my iron golem farm is drowning itself in iron. However, the wheat farm seems to stop working when no one is online, as well as any minecart/redstone builds in the spawn chunks. Is there any mechanic at work here that I overlooked?