I changed my password via my Profile page
That seems unlikely. The "edit" view of your profile page specifies a maxlength which requests that your browser prevent you from typing too long of a password. That same feature is what was preventing you, on one of our 'log in' forms, from entering the 10-character password that you somehow ended up with.
This feature came up a while back when somebody used their own form submission code to change their password and then couldn't use the default site forms to log in. I was hoping you might inform me of some weird way you were able to set too-long of a password.
But, in the mean time, I decided to make the current database restriction on password length (10 characters) be reflected in the password-handling forms of the site (which used to specify a maximum length of 8 characters) because that should eliminate the possibility of having a password that you can't use via the default forms (except for the intentional feature documented in How can I wipe every trace of myself from PerlMonks?).
