why does auto-mounting make files unwritable?
 

I have set most of my drives and partitions to automount. I tried to copy something to one of those partitions, and access was denied. I unmounted and then remounted the partition. That solved the problem. So why would auto-mounting cause that?

'auto-mounting' as such does not cause that. The partitions are being mounted with the read only option. See #man automount