I've had the same issue for over a month - I just use the reset password now to login. Someday I'm sure they'll fix it and then I can set it to a password I can actually remember.
After seeing in a thread from February that old accounts have this issue with the updated forum, hiding the current password field, I used the FireBug plugin in FireFox to make the current password field visible again.
<input id="currentpassword" type="hidden" name="currentpassword">
<input id="currentpassword" type="textbox" name="currentpassword">
This will add a textbox directly under "Edit Email & Password" where you can enter your old password. This won't say "current password" or anything, but it is the quickest and simplest way to get the old password field visible so it can be used for a password change.