Not sure here, but hopefully someone that does know will chime in soon. It is possible that they were designed to work that way, but my guess is you have a broken wire somewhere, probably where the wiring clusters run through some sheetmetal.
Thanks. Just got the van a few months ago and trying to figure out how everything works. I was surprised all doors needed to shut and there was a 5 second delay before they locked. Probably a good idea for me.