I can't reproduce the problem: I tried opening a .capx.backup1 file in WinRAR and pausing it half way through compressing, but Construct 2 could still complete a save without hanging. I'm on Windows 8.1. I don't think it actually updated the .capx.backup1 file, but if another app has it locked then there's no way around that. Still, it worked fine.
Is there another way to reproduce this?