I'm asking nearly the same question, but today is related to my bank website, they disabled several functions, including: right click, copying, pasting.
Is there any real security implication about allowing doing this? Today I was registering an account to do a transfer, and had to type manually the number. Very annoying, to be honest.
I think that they are just exaggerating, I can't see anything wrong about copying my balance or pasting an account number.
Important: They use an on screen keyboard for typing passwords, so copying and pasting passwords is not a reason to do this. This is not the same that related question: Is there any reason to disable paste password on login?