One of the most important things to track in UI design (if you care about a consistent user interface) is all of the nuances which people come to expect.
If you disable the "copy" hot key sequence, then many people will feel frustration because your interface doesn't conform with the nuances that hold for the rest of the operating system. While I understand why you might want to do this, that's not going to convince people that your code isn't broken. After all "Ctrl+c" works every where else.
Once you deviate from enforcing expected UI control nuances, then you need to indicate where the nuance is permitted and where it is denied. That's the DEFINITION of an inconsistent user interface. As the user isn't going to have you there to explain the "why" when the UI does something that they don't expect, they will invariably consider it a bug. If they did have you there telling them why they couldn't do something allowed in every other part of their operating system, they will invariable consider you overzealous in enforcing something stupid which everyone else allows.
The solution is to use a better solution. Enforce what is already expected to reduce the learning curve, or select something (OpenID has been mentioned) that sidesteps the objectionable task(s).