A strong password that gets a lot of its strength from length and mixed case will not still be strong under this error.
For example, the password fOoBaRbAzbArBaZFoO would be a pretty strong password. foobarba is much weaker, and this error would make foobarba (and foobarbaz, etc) work.
A password of that sort is both not that hard to remember and probably fine on a post-it not on the monitor of your home computer. There's really not much overlap between the sorts of people who will break passwords and who will be in a position to read things on your monitor.
(and if they can, some browser password auto-save feature is going to screw you anyway so it doesn't matter)
For example, the password fOoBaRbAzbArBaZFoO would be a pretty strong password. foobarba is much weaker, and this error would make foobarba (and foobarbaz, etc) work.