I set Boinc to limit memory usage to 75% (while in use or not) on an old machine with only 8GB RAM. Attaching to the project Amicable numbers gave me an 8GB task (for my AMD GPU), which locked the whole machine up. Why is it ignoring my preference? The event log stated it was limiting it to 6GB, but I watched it in the task manager rise to 8GB then Windows couldn't handle it.

So I tried 50%. Again, the event log correctly stated 4GB max. Downloaded fresh tasks, this time it seemed to try to limit it, by causing a computation error in the task. Surely I shouldn't have been given these tasks?

This probably has been answered elsewhere but here goes. These tasks require at least 8 GB memory on your motherboard. There is no point in running this project right now if you don't have 16 GB or more ram. Go get some more ram.