What are the settings under Tools > Options > System Options > Performance. Are they the same on both machines.
There may be other settings in the system options that automatically rebuild the assembly. That is the main one I can think of.
Well, on my first test this did indeed seem to correct the issue. I'll test it on some other 'problem' machines, but I think I may have my answer!
Thanks, Jeremy.. so many settings, so little time!!