wp_signon() adds one filter per call

[hakre]

If wp_signon() is called multiple times, the filter will be added multiple times. Next to this a lot of the function seems to be just typed in in the wish that it does work instead of doing things properly. See quote: "ugly hack to pass this to wp_authenticate_cookie" or leftover TODO markings and the like.

Should be put in order prior to next release.

Maybe some code example from that function (too much paranthesis and instructions):

( 0 !== strpos($redirect_to, 'https') ) && ( 0 === strpos($redirect_to, 'http') )

(taken from an if clause therein)

please delete my last comment, I wish I could do that.

Code in function wp_authenticate() might be related.

Only use filter once

Technically this should not be necessary as the new callback would overwrite the previous one because the generate the same hook identification and therefore replace each other.