I had just fed 9 pigmen and started chopping birchnut trees down, but as I was picking up the birchnut nuts they got scared by my proximity and stopped chopping. Similar thing happened to chopping evergreens, but because I wasn't in such a rush to pick up after them, I wasn't jostling them. Also they got interrupted by a sudden treeguard.
*edit to say before the latest update, pigmen would continue chopping unless I am attacked, they are attacked, or food was around, but there was always ample time to pick up the food before they'd break away from chopping, and this felt more like being jostled stopped them from chopping.
I'm on PS4
Feed a (some) pigman.
Start chopping birchnut trees and wait for pigman to start chopping.
Start picking up birhnuts directly behind them.
Observe the pigman loose focus on chopping and run away from you momentarily before idling.