Most likely the cable or the latch itself is a little corroded and binding. Try spraying some lube (preferably some with lithium grease in it) in the latch pivot points and end of the cable and work it back and forth a little to see if it will loosen up. The cable may be binding deeper inside, in which case you may have to take it off to try to gravity feed some lube into it, or replace the cable if that doesn't work.
The return spring could be broken or weak, but it's probably a corrosion/binding problem.
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")