I can write a documentation patch for this:

http://docs.python.org/library/functions.html?highlight=complex#complex

to highlight the expected format of the string argument.

As others have pointed out here, there are a number of other options available to correctly parse the complex string argument:

 * using eval where appropriate; and
 * preprocessing to remove whitespace.

I think that the current options are sufficient that a patch to apply new behaviour isn't required.