Another way to bypass these fields where you can't paste a password (many games are guilty of this atrocity): make an AutoHotkey[1] script for rapidly typing whatever is in your clipboard.
This line will make ctrl-alt-v type your clipboard:
^+v::SendRaw %clipboard%
Seriously, blocking copy & paste, what are they thinking they protect from ?
(blogpost writer here)
If you hit ctrl+v in keepassx it should "autotype" your password for you, bypassing any paste blocking.
oh man. disabling paste is the worst, because it breaks keypassx. (Apple did this last I checked!)
turbotax did that as well last year, this year they made it sane again. Luckily there's a firefox about:config setting you can do to not let websites hijack / block your clipboard events.