Where is this "Form fields" you are refering to? I also can't find any wrench in any way in LastPass account, popup window or any other form of LastPass appearance. I only can see a pencil icon, if you mean that.
All in all, you are right. It feels like it is out of sync with my latest password.
Weirdly enough, if I login with my automated LastPass login it will pop up the message saying that I entered an old password. However, if I select my Lastpass password, press the edit button, then just copy it and paste it in the passowrd area above the previously automated filled password, the number of dots change and then it logs me normally (email remains the same). I only have only one entry with this email but I do have other facebook credentials (for corporal accounts etc), but I never used the same password in other accounts (I always choose "Generate password").