passworded zip

I have a zip file. Inside this file is another zip file (passworded). The file is over 400MB. I have long since forgotten the password, but I have a few clues as to what it might be. On all attempts it has been instant rejection upon wrong password, except for one instance where it starts extracting the whole file and then stops. It extracts to the default temp directory, but by the time it finishes extracting (I assume) it realizes it's the wrong password and the file is deleted.

Now my question is why would it do that? Is that one instance a partially correct password?

Say the instance is 123456, 1234567 causes an instant rejection, 12345 also.

I don't know. I think you can know a password doesn't work early in ZIP files, and that's why they are so easily crackeable. Try Zip Key to crack it, especially if you have a clue of what may it be (what kind of characters and what approximate length).