I'm currently in the process of changing most of my passwords through the Lastpass security challenge, and I ran into a minor hiccup I thought I'd share.
I have the passwords to several Twitter accounts stored in my Lastpass Vault, two of which had to be changed. I let Lastpass change them automatically through the Security Challenge. While changing the second one, I ran into a small issue. Due to my security settings on this particular Twitter account, I was sent a code through a text on my phone which I had to enter to complete the process of changing the password. As Lastpass obviously didn't have access to this code, I had to interfere with the process of auto-renewing the password.
As a result, Lastpass gave an error, stating the password hadn't been changed, even though it did change. The new password was updated by my browser, but not by Lastpass. I also found myself unable to login afterwards; Twitter would only find the passwords saved in my Lastpass Vault, not the ones saved by my browser. As Lastpass hadn't updated the password, I was stuck, and had to manually change the password again. Lastpass then did manage to recognize the password change, and updated the password for this Twitter account.
This was not too much of an issue for myself, but it might be for Lastpass users who aren't very tech savvy. Assuming this was not a bug of some sorts, it might be useful to provide users with a warning before letting Lastpass auto-change a password, to check their security settings for the account in question for any such setting.