First a disclaimer…i am, by no means, an "expert" in the staining of keris. I have done, perhaps, a dozen or so blades, usually to satisfactory results (though my standards and expectations may be low), though often enough had a result that just wasn't acceptable. I believe Alan will tell you it is not unusual to have to stain a blade more than once to get a reasonable result.
I have always used pineapple juice as a cleaning bath an i use that solution straight. So i have no experience with using diluted vinegar. One thing you might try, if you feel that your vinegar must be diluted, is to try using distilled water. It is possible that your water might have a high iron content or some other mineral that is creating such a quickly appearing rust.
Take a good look here to see if you are uploading images correctly.
http://www.vikingsword.com/vb/showthread.php?t=13631