Same problem here. Retina MacBook Pro with an External Display. I run the Parallels window on the External Display and it automatically forces a 199% Zoom under Display Options on Windows 7. You can change it back to 100% (Default), but when you Apply it it makes you log out and back in, and then it's zoomed again.
If I drag the window down to my Retina Display, it looks great. Only issue is that I don't want to run it there, and I need better than 640x480 display resolution on my external monitor.
Cannot find an option to disable this "help" that Parallels is forcing on me. Would have preferred if they just didn't do anything and allowed us to change the zoom ourselves if we so desired. I actually prefer being able to run it at 2880x1800 on my Retina Display, which can only be done with it NOT zoomed.
For me at least, rebooting the VM on the external display does NOT correct the behavior.
Last edited: Aug 31, 2012